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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>34.3. Command Execution Functions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="libpq-status.html" title="34.2. Connection Status Functions" /><link rel="next" href="libpq-async.html" title="34.4. Asynchronous Command Processing" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">34.3. Command Execution Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="libpq-status.html" title="34.2. Connection Status Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="libpq.html" title="Chapter 34. libpq — C Library">Up</a></td><th width="60%" align="center">Chapter 34. <span class="application">libpq</span> — C Library</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.6 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="libpq-async.html" title="34.4. Asynchronous Command Processing">Next</a></td></tr></table><hr /></div><div class="sect1" id="LIBPQ-EXEC"><div class="titlepage"><div><div><h2 class="title" style="clear: both">34.3. Command Execution Functions</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="libpq-exec.html#LIBPQ-EXEC-MAIN">34.3.1. Main Functions</a></span></dt><dt><span class="sect2"><a href="libpq-exec.html#LIBPQ-EXEC-SELECT-INFO">34.3.2. Retrieving Query Result Information</a></span></dt><dt><span class="sect2"><a href="libpq-exec.html#LIBPQ-EXEC-NONSELECT">34.3.3. Retrieving Other Result Information</a></span></dt><dt><span class="sect2"><a href="libpq-exec.html#LIBPQ-EXEC-ESCAPE-STRING">34.3.4. Escaping Strings for Inclusion in SQL Commands</a></span></dt></dl></div><p>
   Once a connection to a database server has been successfully
   established, the functions described here are used to perform
   SQL queries and commands.
  </p><div class="sect2" id="LIBPQ-EXEC-MAIN"><div class="titlepage"><div><div><h3 class="title">34.3.1. Main Functions</h3></div></div></div><p>
    </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQEXEC"><span class="term"><code class="function">PQexec</code><a id="id-1.7.3.10.3.2.1.1.1.2" class="indexterm"></a></span></dt><dd><p>
        Submits a command to the server and waits for the result.

</p><pre class="synopsis">
PGresult *PQexec(PGconn *conn, const char *command);
</pre><p>
       </p><p>
        Returns a <code class="structname">PGresult</code> pointer or possibly a null
        pointer.  A non-null pointer will generally be returned except in
        out-of-memory conditions or serious errors such as inability to send
        the command to the server.  The <a class="xref" href="libpq-exec.html#LIBPQ-PQRESULTSTATUS"><code class="function">PQresultStatus</code></a> function
        should be called to check the return value for any errors (including
        the value of a null pointer, in which case it will return
        <code class="symbol">PGRES_FATAL_ERROR</code>).  Use
        <a class="xref" href="libpq-status.html#LIBPQ-PQERRORMESSAGE"><code class="function">PQerrorMessage</code></a> to get more information about such
        errors.
       </p></dd></dl></div><p>

    The command string can include multiple SQL commands
    (separated by semicolons).  Multiple queries sent in a single
    <a class="xref" href="libpq-exec.html#LIBPQ-PQEXEC"><code class="function">PQexec</code></a> call are processed in a single transaction, unless
    there are explicit <code class="command">BEGIN</code>/<code class="command">COMMIT</code>
    commands included in the query string to divide it into multiple
    transactions.  (See <a class="xref" href="protocol-flow.html#PROTOCOL-FLOW-MULTI-STATEMENT" title="55.2.2.1. Multiple Statements in a Simple Query">Section 55.2.2.1</a>
    for more details about how the server handles multi-query strings.)
    Note however that the returned
    <code class="structname">PGresult</code> structure describes only the result
    of the last command executed from the string.  Should one of the
    commands fail, processing of the string stops with it and the returned
    <code class="structname">PGresult</code> describes the error condition.
   </p><p>
    </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQEXECPARAMS"><span class="term"><code class="function">PQexecParams</code><a id="id-1.7.3.10.3.3.1.1.1.2" class="indexterm"></a></span></dt><dd><p>
        Submits a command to the server and waits for the result,
        with the ability to pass parameters separately from the SQL
        command text.

</p><pre class="synopsis">
PGresult *PQexecParams(PGconn *conn,
                       const char *command,
                       int nParams,
                       const Oid *paramTypes,
                       const char * const *paramValues,
                       const int *paramLengths,
                       const int *paramFormats,
                       int resultFormat);
</pre><p>
       </p><p>
        <a class="xref" href="libpq-exec.html#LIBPQ-PQEXECPARAMS"><code class="function">PQexecParams</code></a> is like <a class="xref" href="libpq-exec.html#LIBPQ-PQEXEC"><code class="function">PQexec</code></a>, but offers additional
        functionality: parameter values can be specified separately from the command
        string proper, and query results can be requested in either text or binary
        format.
       </p><p>
        The function arguments are:

        </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>conn</code></em></span></dt><dd><p>
            The connection object to send the command through.
           </p></dd><dt><span class="term"><em class="parameter"><code>command</code></em></span></dt><dd><p>
            The SQL command string to be executed. If parameters are used,
            they are referred to in the command string as <code class="literal">$1</code>,
            <code class="literal">$2</code>, etc.
           </p></dd><dt><span class="term"><em class="parameter"><code>nParams</code></em></span></dt><dd><p>
            The number of parameters supplied; it is the length of the arrays
            <em class="parameter"><code>paramTypes[]</code></em>, <em class="parameter"><code>paramValues[]</code></em>,
            <em class="parameter"><code>paramLengths[]</code></em>, and <em class="parameter"><code>paramFormats[]</code></em>. (The
            array pointers can be <code class="symbol">NULL</code> when <em class="parameter"><code>nParams</code></em>
            is zero.)
           </p></dd><dt><span class="term"><em class="parameter"><code>paramTypes[]</code></em></span></dt><dd><p>
            Specifies, by OID, the data types to be assigned to the
            parameter symbols.  If <em class="parameter"><code>paramTypes</code></em> is
            <code class="symbol">NULL</code>, or any particular element in the array
            is zero, the server infers a data type for the parameter symbol
            in the same way it would do for an untyped literal string.
           </p></dd><dt><span class="term"><em class="parameter"><code>paramValues[]</code></em></span></dt><dd><p>
            Specifies the actual values of the parameters.  A null pointer
            in this array means the corresponding parameter is null;
            otherwise the pointer points to a zero-terminated text string
            (for text format) or binary data in the format expected by the
            server (for binary format).
           </p></dd><dt><span class="term"><em class="parameter"><code>paramLengths[]</code></em></span></dt><dd><p>
            Specifies the actual data lengths of binary-format parameters.
            It is ignored for null parameters and text-format parameters.
            The array pointer can be null when there are no binary parameters.
           </p></dd><dt><span class="term"><em class="parameter"><code>paramFormats[]</code></em></span></dt><dd><p>
            Specifies whether parameters are text (put a zero in the
            array entry for the corresponding parameter) or binary (put
            a one in the array entry for the corresponding parameter).
            If the array pointer is null then all parameters are presumed
            to be text strings.
           </p><p>
            Values passed in binary format require knowledge of
            the internal representation expected by the backend.
            For example, integers must be passed in network byte
            order.  Passing <code class="type">numeric</code> values requires
            knowledge of the server storage format, as implemented
            in
            <code class="filename">src/backend/utils/adt/numeric.c::numeric_send()</code> and
            <code class="filename">src/backend/utils/adt/numeric.c::numeric_recv()</code>.
           </p></dd><dt><span class="term"><em class="parameter"><code>resultFormat</code></em></span></dt><dd><p>
            Specify zero to obtain results in text format, or one to obtain
            results in binary format.  (There is not currently a provision
            to obtain different result columns in different formats,
            although that is possible in the underlying protocol.)
           </p></dd></dl></div><p>
       </p></dd></dl></div><p>
   </p><p>
    The primary advantage of <a class="xref" href="libpq-exec.html#LIBPQ-PQEXECPARAMS"><code class="function">PQexecParams</code></a> over
    <a class="xref" href="libpq-exec.html#LIBPQ-PQEXEC"><code class="function">PQexec</code></a> is that parameter values can be separated from the
    command string, thus avoiding the need for tedious and error-prone
    quoting and escaping.
   </p><p>
    Unlike <a class="xref" href="libpq-exec.html#LIBPQ-PQEXEC"><code class="function">PQexec</code></a>, <a class="xref" href="libpq-exec.html#LIBPQ-PQEXECPARAMS"><code class="function">PQexecParams</code></a> allows at most
    one SQL command in the given string.  (There can be semicolons in it,
    but not more than one nonempty command.)  This is a limitation of the
    underlying protocol, but has some usefulness as an extra defense against
    SQL-injection attacks.
   </p><div class="tip"><h3 class="title">Tip</h3><p>
     Specifying parameter types via OIDs is tedious, particularly if you prefer
     not to hard-wire particular OID values into your program.  However, you can
     avoid doing so even in cases where the server by itself cannot determine the
     type of the parameter, or chooses a different type than you want.  In the
     SQL command text, attach an explicit cast to the parameter symbol to show what
     data type you will send.  For example:
</p><pre class="programlisting">
SELECT * FROM mytable WHERE x = $1::bigint;
</pre><p>
     This forces parameter <code class="literal">$1</code> to be treated as <code class="type">bigint</code>, whereas
     by default it would be assigned the same type as <code class="literal">x</code>.  Forcing the
     parameter type decision, either this way or by specifying a numeric type OID,
     is strongly recommended when sending parameter values in binary format, because
     binary format has less redundancy than text format and so there is less chance
     that the server will detect a type mismatch mistake for you.
    </p></div><p>
    </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQPREPARE"><span class="term"><code class="function">PQprepare</code><a id="id-1.7.3.10.3.7.1.1.1.2" class="indexterm"></a></span></dt><dd><p>
        Submits a request to create a prepared statement with the
        given parameters, and waits for completion.
</p><pre class="synopsis">
PGresult *PQprepare(PGconn *conn,
                    const char *stmtName,
                    const char *query,
                    int nParams,
                    const Oid *paramTypes);
</pre><p>
       </p><p>
        <a class="xref" href="libpq-exec.html#LIBPQ-PQPREPARE"><code class="function">PQprepare</code></a> creates a prepared statement for later
        execution with <a class="xref" href="libpq-exec.html#LIBPQ-PQEXECPREPARED"><code class="function">PQexecPrepared</code></a>.  This feature allows
        commands to be executed repeatedly without being parsed and
        planned each time;  see <a class="xref" href="sql-prepare.html" title="PREPARE"><span class="refentrytitle">PREPARE</span></a> for details.
       </p><p>
        The function creates a prepared statement named
        <em class="parameter"><code>stmtName</code></em> from the <em class="parameter"><code>query</code></em> string, which
        must contain a single SQL command.  <em class="parameter"><code>stmtName</code></em> can be
        <code class="literal">""</code> to create an unnamed statement, in which case any
        pre-existing unnamed statement is automatically replaced; otherwise
        it is an error if the statement name is already defined in the
        current session.  If any parameters are used, they are referred
        to in the query as <code class="literal">$1</code>, <code class="literal">$2</code>, etc.
        <em class="parameter"><code>nParams</code></em> is the number of parameters for which types
        are pre-specified in the array <em class="parameter"><code>paramTypes[]</code></em>.  (The
        array pointer can be <code class="symbol">NULL</code> when
        <em class="parameter"><code>nParams</code></em> is zero.) <em class="parameter"><code>paramTypes[]</code></em>
        specifies, by OID, the data types to be assigned to the parameter
        symbols.  If <em class="parameter"><code>paramTypes</code></em> is <code class="symbol">NULL</code>,
        or any particular element in the array is zero, the server assigns
        a data type to the parameter symbol in the same way it would do
        for an untyped literal string.  Also, the query can use parameter
        symbols with numbers higher than <em class="parameter"><code>nParams</code></em>; data types
        will be inferred for these symbols as well.  (See
        <a class="xref" href="libpq-exec.html#LIBPQ-PQDESCRIBEPREPARED"><code class="function">PQdescribePrepared</code></a> for a means to find out
        what data types were inferred.)
       </p><p>
        As with <a class="xref" href="libpq-exec.html#LIBPQ-PQEXEC"><code class="function">PQexec</code></a>, the result is normally a
        <code class="structname">PGresult</code> object whose contents indicate
        server-side success or failure.  A null result indicates
        out-of-memory or inability to send the command at all.  Use
        <a class="xref" href="libpq-status.html#LIBPQ-PQERRORMESSAGE"><code class="function">PQerrorMessage</code></a> to get more information about
        such errors.
       </p></dd></dl></div><p>

    Prepared statements for use with <a class="xref" href="libpq-exec.html#LIBPQ-PQEXECPREPARED"><code class="function">PQexecPrepared</code></a> can also
    be created by executing SQL <a class="xref" href="sql-prepare.html" title="PREPARE"><span class="refentrytitle">PREPARE</span></a>
    statements.  Also, although there is no <span class="application">libpq</span>
    function for deleting a prepared statement, the SQL <a class="xref" href="sql-deallocate.html" title="DEALLOCATE"><span class="refentrytitle">DEALLOCATE</span></a> statement
    can be used for that purpose.
   </p><p>
    </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQEXECPREPARED"><span class="term"><code class="function">PQexecPrepared</code><a id="id-1.7.3.10.3.8.1.1.1.2" class="indexterm"></a></span></dt><dd><p>
        Sends a request to execute a prepared statement with given
        parameters, and waits for the result.
</p><pre class="synopsis">
PGresult *PQexecPrepared(PGconn *conn,
                         const char *stmtName,
                         int nParams,
                         const char * const *paramValues,
                         const int *paramLengths,
                         const int *paramFormats,
                         int resultFormat);
</pre><p>
       </p><p>
        <a class="xref" href="libpq-exec.html#LIBPQ-PQEXECPREPARED"><code class="function">PQexecPrepared</code></a> is like <a class="xref" href="libpq-exec.html#LIBPQ-PQEXECPARAMS"><code class="function">PQexecParams</code></a>,
        but the command to be executed is specified by naming a
        previously-prepared statement, instead of giving a query string.
        This feature allows commands that will be used repeatedly to be
        parsed and planned just once, rather than each time they are
        executed.  The statement must have been prepared previously in
        the current session.
       </p><p>
        The parameters are identical to <a class="xref" href="libpq-exec.html#LIBPQ-PQEXECPARAMS"><code class="function">PQexecParams</code></a>, except that the
        name of a prepared statement is given instead of a query string, and the
        <em class="parameter"><code>paramTypes[]</code></em> parameter is not present (it is not needed since
        the prepared statement's parameter types were determined when it was created).
       </p></dd><dt id="LIBPQ-PQDESCRIBEPREPARED"><span class="term"><code class="function">PQdescribePrepared</code><a id="id-1.7.3.10.3.8.1.2.1.2" class="indexterm"></a></span></dt><dd><p>
        Submits a request to obtain information about the specified
        prepared statement, and waits for completion.
</p><pre class="synopsis">
PGresult *PQdescribePrepared(PGconn *conn, const char *stmtName);
</pre><p>
       </p><p>
        <a class="xref" href="libpq-exec.html#LIBPQ-PQDESCRIBEPREPARED"><code class="function">PQdescribePrepared</code></a> allows an application to obtain
        information about a previously prepared statement.
       </p><p>
        <em class="parameter"><code>stmtName</code></em> can be <code class="literal">""</code> or <code class="symbol">NULL</code> to reference
        the unnamed statement, otherwise it must be the name of an existing
        prepared statement.  On success, a <code class="structname">PGresult</code> with
        status <code class="literal">PGRES_COMMAND_OK</code> is returned.  The
        functions <a class="xref" href="libpq-exec.html#LIBPQ-PQNPARAMS"><code class="function">PQnparams</code></a> and
        <a class="xref" href="libpq-exec.html#LIBPQ-PQPARAMTYPE"><code class="function">PQparamtype</code></a> can be applied to this
        <code class="structname">PGresult</code> to obtain information about the parameters
        of the prepared statement, and the functions
        <a class="xref" href="libpq-exec.html#LIBPQ-PQNFIELDS"><code class="function">PQnfields</code></a>, <a class="xref" href="libpq-exec.html#LIBPQ-PQFNAME"><code class="function">PQfname</code></a>,
        <a class="xref" href="libpq-exec.html#LIBPQ-PQFTYPE"><code class="function">PQftype</code></a>, etc. provide information about the
        result columns (if any) of the statement.
       </p></dd><dt id="LIBPQ-PQDESCRIBEPORTAL"><span class="term"><code class="function">PQdescribePortal</code><a id="id-1.7.3.10.3.8.1.3.1.2" class="indexterm"></a></span></dt><dd><p>
        Submits a request to obtain information about the specified
        portal, and waits for completion.
</p><pre class="synopsis">
PGresult *PQdescribePortal(PGconn *conn, const char *portalName);
</pre><p>
       </p><p>
        <a class="xref" href="libpq-exec.html#LIBPQ-PQDESCRIBEPORTAL"><code class="function">PQdescribePortal</code></a> allows an application to obtain
        information about a previously created portal.
        (<span class="application">libpq</span> does not provide any direct access to
        portals, but you can use this function to inspect the properties
        of a cursor created with a <code class="command">DECLARE CURSOR</code> SQL command.)
       </p><p>
        <em class="parameter"><code>portalName</code></em> can be <code class="literal">""</code> or <code class="symbol">NULL</code> to reference
        the unnamed portal, otherwise it must be the name of an existing
        portal.  On success, a <code class="structname">PGresult</code> with status
        <code class="literal">PGRES_COMMAND_OK</code> is returned.  The functions
        <a class="xref" href="libpq-exec.html#LIBPQ-PQNFIELDS"><code class="function">PQnfields</code></a>, <a class="xref" href="libpq-exec.html#LIBPQ-PQFNAME"><code class="function">PQfname</code></a>,
        <a class="xref" href="libpq-exec.html#LIBPQ-PQFTYPE"><code class="function">PQftype</code></a>, etc. can be applied to the
        <code class="structname">PGresult</code> to obtain information about the result
        columns (if any) of the portal.
       </p></dd></dl></div><p>
   </p><p>
    The <code class="structname">PGresult</code><a id="id-1.7.3.10.3.9.2" class="indexterm"></a>
    structure encapsulates the result returned by the server.
    <span class="application">libpq</span> application programmers should be
    careful to maintain the <code class="structname">PGresult</code> abstraction.
    Use the accessor functions below to get at the contents of
    <code class="structname">PGresult</code>.  Avoid directly referencing the
    fields of the <code class="structname">PGresult</code> structure because they
    are subject to change in the future.

    </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQRESULTSTATUS"><span class="term"><code class="function">PQresultStatus</code><a id="id-1.7.3.10.3.9.7.1.1.2" class="indexterm"></a></span></dt><dd><p>
        Returns the result status of the command.
</p><pre class="synopsis">
ExecStatusType PQresultStatus(const PGresult *res);
</pre><p>
       </p><p>
        <a class="xref" href="libpq-exec.html#LIBPQ-PQRESULTSTATUS"><code class="function">PQresultStatus</code></a> can return one of the following values:

        </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PGRES-EMPTY-QUERY"><span class="term"><code class="literal">PGRES_EMPTY_QUERY</code></span></dt><dd><p>
            The string sent to the server was empty.
           </p></dd><dt id="LIBPQ-PGRES-COMMAND-OK"><span class="term"><code class="literal">PGRES_COMMAND_OK</code></span></dt><dd><p>
            Successful completion of a command returning no data.
           </p></dd><dt id="LIBPQ-PGRES-TUPLES-OK"><span class="term"><code class="literal">PGRES_TUPLES_OK</code></span></dt><dd><p>
            Successful completion of a command returning data (such as
            a <code class="command">SELECT</code> or <code class="command">SHOW</code>).
           </p></dd><dt id="LIBPQ-PGRES-COPY-OUT"><span class="term"><code class="literal">PGRES_COPY_OUT</code></span></dt><dd><p>
            Copy Out (from server) data transfer started.
           </p></dd><dt id="LIBPQ-PGRES-COPY-IN"><span class="term"><code class="literal">PGRES_COPY_IN</code></span></dt><dd><p>
            Copy In (to server) data transfer started.
           </p></dd><dt id="LIBPQ-PGRES-BAD-RESPONSE"><span class="term"><code class="literal">PGRES_BAD_RESPONSE</code></span></dt><dd><p>
            The server's response was not understood.
           </p></dd><dt id="LIBPQ-PGRES-NONFATAL-ERROR"><span class="term"><code class="literal">PGRES_NONFATAL_ERROR</code></span></dt><dd><p>
            A nonfatal error (a notice or warning) occurred.
           </p></dd><dt id="LIBPQ-PGRES-FATAL-ERROR"><span class="term"><code class="literal">PGRES_FATAL_ERROR</code></span></dt><dd><p>
            A fatal error occurred.
           </p></dd><dt id="LIBPQ-PGRES-COPY-BOTH"><span class="term"><code class="literal">PGRES_COPY_BOTH</code></span></dt><dd><p>
            Copy In/Out (to and from server) data transfer started.  This
            feature is currently used only for streaming replication,
            so this status should not occur in ordinary applications.
           </p></dd><dt id="LIBPQ-PGRES-SINGLE-TUPLE"><span class="term"><code class="literal">PGRES_SINGLE_TUPLE</code></span></dt><dd><p>
            The <code class="structname">PGresult</code> contains a single result tuple
            from the current command.  This status occurs only when
            single-row mode has been selected for the query
            (see <a class="xref" href="libpq-single-row-mode.html" title="34.6. Retrieving Query Results Row-by-Row">Section 34.6</a>).
           </p></dd><dt id="LIBPQ-PGRES-PIPELINE-SYNC"><span class="term"><code class="literal">PGRES_PIPELINE_SYNC</code></span></dt><dd><p>
            The <code class="structname">PGresult</code> represents a
            synchronization point in pipeline mode, requested by
            <a class="xref" href="libpq-pipeline-mode.html#LIBPQ-PQPIPELINESYNC"><code class="function">PQpipelineSync</code></a>.
            This status occurs only when pipeline mode has been selected.
           </p></dd><dt id="LIBPQ-PGRES-PIPELINE-ABORTED"><span class="term"><code class="literal">PGRES_PIPELINE_ABORTED</code></span></dt><dd><p>
            The <code class="structname">PGresult</code> represents a pipeline that has
            received an error from the server.  <code class="function">PQgetResult</code>
            must be called repeatedly, and each time it will return this status code
            until the end of the current pipeline, at which point it will return
            <code class="literal">PGRES_PIPELINE_SYNC</code> and normal processing can
            resume.
           </p></dd></dl></div><p>

        If the result status is <code class="literal">PGRES_TUPLES_OK</code> or
        <code class="literal">PGRES_SINGLE_TUPLE</code>, then
        the functions described below can be used to retrieve the rows
        returned by the query.  Note that a <code class="command">SELECT</code>
        command that happens to retrieve zero rows still shows
        <code class="literal">PGRES_TUPLES_OK</code>.
        <code class="literal">PGRES_COMMAND_OK</code> is for commands that can never
        return rows (<code class="command">INSERT</code> or <code class="command">UPDATE</code>
        without a <code class="literal">RETURNING</code> clause,
        etc.). A response of <code class="literal">PGRES_EMPTY_QUERY</code> might
        indicate a bug in the client software.
       </p><p>
        A result of status <code class="symbol">PGRES_NONFATAL_ERROR</code> will
        never be returned directly by <a class="xref" href="libpq-exec.html#LIBPQ-PQEXEC"><code class="function">PQexec</code></a> or other
        query execution functions; results of this kind are instead passed
        to the notice processor (see <a class="xref" href="libpq-notice-processing.html" title="34.13. Notice Processing">Section 34.13</a>).
       </p></dd><dt id="LIBPQ-PQRESSTATUS"><span class="term"><code class="function">PQresStatus</code><a id="id-1.7.3.10.3.9.7.2.1.2" class="indexterm"></a></span></dt><dd><p>
        Converts the enumerated type returned by
        <a class="xref" href="libpq-exec.html#LIBPQ-PQRESULTSTATUS"><code class="function">PQresultStatus</code></a> into a string constant describing the
        status code. The caller should not free the result.

</p><pre class="synopsis">
char *PQresStatus(ExecStatusType status);
</pre><p>
       </p></dd><dt id="LIBPQ-PQRESULTERRORMESSAGE"><span class="term"><code class="function">PQresultErrorMessage</code><a id="id-1.7.3.10.3.9.7.3.1.2" class="indexterm"></a></span></dt><dd><p>
        Returns the error message associated with the command, or an empty string
        if there was no error.
</p><pre class="synopsis">
char *PQresultErrorMessage(const PGresult *res);
</pre><p>
        If there was an error, the returned string will include a trailing
        newline.  The caller should not free the result directly. It will
        be freed when the associated <code class="structname">PGresult</code> handle is
        passed to <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a>.
       </p><p>
        Immediately following a <a class="xref" href="libpq-exec.html#LIBPQ-PQEXEC"><code class="function">PQexec</code></a> or
        <a class="xref" href="libpq-async.html#LIBPQ-PQGETRESULT"><code class="function">PQgetResult</code></a> call,
        <a class="xref" href="libpq-status.html#LIBPQ-PQERRORMESSAGE"><code class="function">PQerrorMessage</code></a> (on the connection) will return
        the same string as <a class="xref" href="libpq-exec.html#LIBPQ-PQRESULTERRORMESSAGE"><code class="function">PQresultErrorMessage</code></a> (on
        the result).  However, a <code class="structname">PGresult</code> will
        retain its error message until destroyed, whereas the connection's
        error message will change when subsequent operations are done.
        Use <a class="xref" href="libpq-exec.html#LIBPQ-PQRESULTERRORMESSAGE"><code class="function">PQresultErrorMessage</code></a> when you want to
        know the status associated with a particular
        <code class="structname">PGresult</code>; use
        <a class="xref" href="libpq-status.html#LIBPQ-PQERRORMESSAGE"><code class="function">PQerrorMessage</code></a> when you want to know the
        status from the latest operation on the connection.
       </p></dd><dt id="LIBPQ-PQRESULTVERBOSEERRORMESSAGE"><span class="term"><code class="function">PQresultVerboseErrorMessage</code><a id="id-1.7.3.10.3.9.7.4.1.2" class="indexterm"></a></span></dt><dd><p>
        Returns a reformatted version of the error message associated with
        a <code class="structname">PGresult</code> object.
</p><pre class="synopsis">
char *PQresultVerboseErrorMessage(const PGresult *res,
                                  PGVerbosity verbosity,
                                  PGContextVisibility show_context);
</pre><p>
        In some situations a client might wish to obtain a more detailed
        version of a previously-reported error.
        <a class="xref" href="libpq-exec.html#LIBPQ-PQRESULTVERBOSEERRORMESSAGE"><code class="function">PQresultVerboseErrorMessage</code></a> addresses this need
        by computing the message that would have been produced
        by <a class="xref" href="libpq-exec.html#LIBPQ-PQRESULTERRORMESSAGE"><code class="function">PQresultErrorMessage</code></a> if the specified
        verbosity settings had been in effect for the connection when the
        given <code class="structname">PGresult</code> was generated.  If
        the <code class="structname">PGresult</code> is not an error result,
        <span class="quote"><span class="quote">PGresult is not an error result</span></span> is reported instead.
        The returned string includes a trailing newline.
       </p><p>
        Unlike most other functions for extracting data from
        a <code class="structname">PGresult</code>, the result of this function is a freshly
        allocated string.  The caller must free it
        using <code class="function">PQfreemem()</code> when the string is no longer needed.
       </p><p>
        A NULL return is possible if there is insufficient memory.
       </p></dd><dt id="LIBPQ-PQRESULTERRORFIELD"><span class="term"><code class="function">PQresultErrorField</code><a id="id-1.7.3.10.3.9.7.5.1.2" class="indexterm"></a></span></dt><dd><p>
        Returns an individual field of an error report.
</p><pre class="synopsis">
char *PQresultErrorField(const PGresult *res, int fieldcode);
</pre><p>
        <em class="parameter"><code>fieldcode</code></em> is an error field identifier; see the symbols
        listed below.  <code class="symbol">NULL</code> is returned if the
        <code class="structname">PGresult</code> is not an error or warning result,
        or does not include the specified field.  Field values will normally
        not include a trailing newline. The caller should not free the
        result directly. It will be freed when the
        associated <code class="structname">PGresult</code> handle is passed to
        <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a>.
       </p><p>
        The following field codes are available:
        </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PG-DIAG-SEVERITY"><span class="term"><code class="symbol">PG_DIAG_SEVERITY</code></span></dt><dd><p>
            The severity; the field contents are <code class="literal">ERROR</code>,
            <code class="literal">FATAL</code>, or <code class="literal">PANIC</code> (in an error message),
            or <code class="literal">WARNING</code>, <code class="literal">NOTICE</code>, <code class="literal">DEBUG</code>,
            <code class="literal">INFO</code>, or <code class="literal">LOG</code> (in a notice message), or
            a localized translation of one of these.  Always present.
           </p></dd><dt id="LIBPQ-PG-DIAG-SEVERITY-NONLOCALIZED"><span class="term"><code class="symbol">PG_DIAG_SEVERITY_NONLOCALIZED</code></span></dt><dd><p>
            The severity; the field contents are <code class="literal">ERROR</code>,
            <code class="literal">FATAL</code>, or <code class="literal">PANIC</code> (in an error message),
            or <code class="literal">WARNING</code>, <code class="literal">NOTICE</code>, <code class="literal">DEBUG</code>,
            <code class="literal">INFO</code>, or <code class="literal">LOG</code> (in a notice message).
            This is identical to the <code class="symbol">PG_DIAG_SEVERITY</code> field except
            that the contents are never localized.  This is present only in
            reports generated by <span class="productname">PostgreSQL</span> versions 9.6
            and later.
           </p></dd><dt id="LIBPQ-PG-DIAG-SQLSTATE"><span class="term"><code class="symbol">PG_DIAG_SQLSTATE</code><a id="id-1.7.3.10.3.9.7.5.2.2.1.3.1.2" class="indexterm"></a></span></dt><dd><p>
            The SQLSTATE code for the error. The SQLSTATE code identifies
            the type of error that has occurred; it can be used by
            front-end applications to perform specific operations (such
            as error handling) in response to a particular database error.
            For a list of the possible SQLSTATE codes, see <a class="xref" href="errcodes-appendix.html" title="Appendix A. PostgreSQL Error Codes">Appendix A</a>. This field is not localizable,
            and is always present.
           </p></dd><dt id="LIBPQ-PG-DIAG-MESSAGE-PRIMARY"><span class="term"><code class="symbol">PG_DIAG_MESSAGE_PRIMARY</code></span></dt><dd><p>
            The primary human-readable error message (typically one line).
            Always present.
           </p></dd><dt id="LIBPQ-PG-DIAG-MESSAGE-DETAIL"><span class="term"><code class="symbol">PG_DIAG_MESSAGE_DETAIL</code></span></dt><dd><p>
            Detail: an optional secondary error message carrying more
            detail about the problem.  Might run to multiple lines.
           </p></dd><dt id="LIBPQ-PG-DIAG-MESSAGE-HINT"><span class="term"><code class="symbol">PG_DIAG_MESSAGE_HINT</code></span></dt><dd><p>
            Hint: an optional suggestion what to do about the problem.
            This is intended to differ from detail in that it offers advice
            (potentially inappropriate) rather than hard facts.  Might
            run to multiple lines.
           </p></dd><dt id="LIBPQ-PG-DIAG-STATEMENT-POSITION"><span class="term"><code class="symbol">PG_DIAG_STATEMENT_POSITION</code></span></dt><dd><p>
            A string containing a decimal integer indicating an error cursor
            position as an index into the original statement string.  The
            first character has index 1, and positions are measured in
            characters not bytes.
           </p></dd><dt id="LIBPQ-PG-DIAG-INTERNAL-POSITION"><span class="term"><code class="symbol">PG_DIAG_INTERNAL_POSITION</code></span></dt><dd><p>
            This is defined the same as the
            <code class="symbol">PG_DIAG_STATEMENT_POSITION</code> field, but it is used
            when the cursor position refers to an internally generated
            command rather than the one submitted by the client.  The
            <code class="symbol">PG_DIAG_INTERNAL_QUERY</code> field will always appear when
            this field appears.
           </p></dd><dt id="LIBPQ-PG-DIAG-INTERNAL-QUERY"><span class="term"><code class="symbol">PG_DIAG_INTERNAL_QUERY</code></span></dt><dd><p>
            The text of a failed internally-generated command.  This could
            be, for example, an SQL query issued by a PL/pgSQL function.
           </p></dd><dt id="LIBPQ-PG-DIAG-CONTEXT"><span class="term"><code class="symbol">PG_DIAG_CONTEXT</code></span></dt><dd><p>
            An indication of the context in which the error occurred.
            Presently this includes a call stack traceback of active
            procedural language functions and internally-generated queries.
            The trace is one entry per line, most recent first.
           </p></dd><dt id="LIBPQ-PG-DIAG-SCHEMA-NAME"><span class="term"><code class="symbol">PG_DIAG_SCHEMA_NAME</code></span></dt><dd><p>
            If the error was associated with a specific database object,
            the name of the schema containing that object, if any.
           </p></dd><dt id="LIBPQ-PG-DIAG-TABLE-NAME"><span class="term"><code class="symbol">PG_DIAG_TABLE_NAME</code></span></dt><dd><p>
            If the error was associated with a specific table, the name of the
            table.  (Refer to the schema name field for the name of the
            table's schema.)
           </p></dd><dt id="LIBPQ-PG-DIAG-COLUMN-NAME"><span class="term"><code class="symbol">PG_DIAG_COLUMN_NAME</code></span></dt><dd><p>
            If the error was associated with a specific table column, the name
            of the column.  (Refer to the schema and table name fields to
            identify the table.)
           </p></dd><dt id="LIBPQ-PG-DIAG-DATATYPE-NAME"><span class="term"><code class="symbol">PG_DIAG_DATATYPE_NAME</code></span></dt><dd><p>
            If the error was associated with a specific data type, the name of
            the data type.  (Refer to the schema name field for the name of
            the data type's schema.)
           </p></dd><dt id="LIBPQ-PG-DIAG-CONSTRAINT-NAME"><span class="term"><code class="symbol">PG_DIAG_CONSTRAINT_NAME</code></span></dt><dd><p>
            If the error was associated with a specific constraint, the name
            of the constraint.  Refer to fields listed above for the
            associated table or domain.  (For this purpose, indexes are
            treated as constraints, even if they weren't created with
            constraint syntax.)
           </p></dd><dt id="LIBPQ-PG-DIAG-SOURCE-FILE"><span class="term"><code class="symbol">PG_DIAG_SOURCE_FILE</code></span></dt><dd><p>
            The file name of the source-code location where the error was
            reported.
           </p></dd><dt id="LIBPQ-PG-DIAG-SOURCE-LINE"><span class="term"><code class="symbol">PG_DIAG_SOURCE_LINE</code></span></dt><dd><p>
            The line number of the source-code location where the error
            was reported.
           </p></dd><dt id="LIBPQ-PG-DIAG-SOURCE-FUNCTION"><span class="term"><code class="symbol">PG_DIAG_SOURCE_FUNCTION</code></span></dt><dd><p>
            The name of the source-code function reporting the error.
           </p></dd></dl></div><p>
       </p><div class="note"><h3 class="title">Note</h3><p>
         The fields for schema name, table name, column name, data type name,
         and constraint name are supplied only for a limited number of error
         types; see <a class="xref" href="errcodes-appendix.html" title="Appendix A. PostgreSQL Error Codes">Appendix A</a>.  Do not assume that
         the presence of any of these fields guarantees the presence of
         another field.  Core error sources observe the interrelationships
         noted above, but user-defined functions may use these fields in other
         ways.  In the same vein, do not assume that these fields denote
         contemporary objects in the current database.
        </p></div><p>
        The client is responsible for formatting displayed information to meet
        its needs; in particular it should break long lines as needed.
        Newline characters appearing in the error message fields should be
        treated as paragraph breaks, not line breaks.
       </p><p>
        Errors generated internally by <span class="application">libpq</span> will
        have severity and primary message, but typically no other fields.
       </p><p>
        Note that error fields are only available from
        <code class="structname">PGresult</code> objects, not
        <code class="structname">PGconn</code> objects; there is no
        <code class="function">PQerrorField</code> function.
       </p></dd><dt id="LIBPQ-PQCLEAR"><span class="term"><code class="function">PQclear</code><a id="id-1.7.3.10.3.9.7.6.1.2" class="indexterm"></a></span></dt><dd><p>
        Frees  the  storage  associated with a
        <code class="structname">PGresult</code>.  Every command result should be
        freed via <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a> when it  is  no  longer
        needed.

</p><pre class="synopsis">
void PQclear(PGresult *res);
</pre><p>
       </p><p>
        You can keep a <code class="structname">PGresult</code> object around for
        as long as you need it; it does not go away when you issue a new
        command, nor even if you close the connection.  To get rid of it,
        you must call <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a>.  Failure to do this
        will result in memory leaks in your application.
       </p></dd></dl></div><p>
   </p></div><div class="sect2" id="LIBPQ-EXEC-SELECT-INFO"><div class="titlepage"><div><div><h3 class="title">34.3.2. Retrieving Query Result Information</h3></div></div></div><p>
    These functions are used to extract information from a
    <code class="structname">PGresult</code> object that represents a successful
    query result (that is, one that has status
    <code class="literal">PGRES_TUPLES_OK</code> or <code class="literal">PGRES_SINGLE_TUPLE</code>).
    They can also be used to extract
    information from a successful Describe operation: a Describe's result
    has all the same column information that actual execution of the query
    would provide, but it has zero rows.  For objects with other status values,
    these functions will act as though the result has zero rows and zero columns.
   </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQNTUPLES"><span class="term"><code class="function">PQntuples</code><a id="id-1.7.3.10.4.3.1.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the number of rows (tuples) in the query result.
       (Note that <code class="structname">PGresult</code> objects are limited to no more
       than <code class="literal">INT_MAX</code> rows, so an <code class="type">int</code> result is
       sufficient.)

</p><pre class="synopsis">
int PQntuples(const PGresult *res);
</pre><p>

      </p></dd><dt id="LIBPQ-PQNFIELDS"><span class="term"><code class="function">PQnfields</code><a id="id-1.7.3.10.4.3.2.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the number of columns (fields) in each row of the query
       result.

</p><pre class="synopsis">
int PQnfields(const PGresult *res);
</pre><p>
      </p></dd><dt id="LIBPQ-PQFNAME"><span class="term"><code class="function">PQfname</code><a id="id-1.7.3.10.4.3.3.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the column name associated with the given column number.
       Column numbers start at 0. The caller should not free the result
       directly. It will be freed when the associated
       <code class="structname">PGresult</code> handle is passed to
       <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a>.
</p><pre class="synopsis">
char *PQfname(const PGresult *res,
              int column_number);
</pre><p>
      </p><p>
       <code class="symbol">NULL</code> is returned if the column number is out of range.
      </p></dd><dt id="LIBPQ-PQFNUMBER"><span class="term"><code class="function">PQfnumber</code><a id="id-1.7.3.10.4.3.4.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the column number associated with the given column name.
</p><pre class="synopsis">
int PQfnumber(const PGresult *res,
              const char *column_name);
</pre><p>
      </p><p>
       -1 is returned if the given name does not match any column.
      </p><p>
       The given name is treated like an identifier in an SQL command,
       that is, it is downcased unless double-quoted.  For example, given
       a query result generated from the SQL command:
</p><pre class="programlisting">
SELECT 1 AS FOO, 2 AS "BAR";
</pre><p>
       we would have the results:
</p><pre class="programlisting">
PQfname(res, 0)              <em class="lineannotation"><span class="lineannotation">foo</span></em>
PQfname(res, 1)              <em class="lineannotation"><span class="lineannotation">BAR</span></em>
PQfnumber(res, "FOO")        <em class="lineannotation"><span class="lineannotation">0</span></em>
PQfnumber(res, "foo")        <em class="lineannotation"><span class="lineannotation">0</span></em>
PQfnumber(res, "BAR")        <em class="lineannotation"><span class="lineannotation">-1</span></em>
PQfnumber(res, "\"BAR\"")    <em class="lineannotation"><span class="lineannotation">1</span></em>
</pre><p>
      </p></dd><dt id="LIBPQ-PQFTABLE"><span class="term"><code class="function">PQftable</code><a id="id-1.7.3.10.4.3.5.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the OID of the table from which the given column was
       fetched.  Column numbers start at 0.
</p><pre class="synopsis">
Oid PQftable(const PGresult *res,
             int column_number);
</pre><p>
      </p><p>
       <code class="literal">InvalidOid</code> is returned if the column number is out of range,
       or if the specified column is not a simple reference to a table column.
       You can query the system table <code class="literal">pg_class</code> to determine
       exactly which table is referenced.
      </p><p>
       The type <code class="type">Oid</code> and the constant
       <code class="literal">InvalidOid</code> will be defined when you include
       the <span class="application">libpq</span> header file. They will both
       be some integer type.
      </p></dd><dt id="LIBPQ-PQFTABLECOL"><span class="term"><code class="function">PQftablecol</code><a id="id-1.7.3.10.4.3.6.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the column number (within its table) of the column making
       up the specified query result column.  Query-result column numbers
       start at 0, but table columns have nonzero numbers.
</p><pre class="synopsis">
int PQftablecol(const PGresult *res,
                int column_number);
</pre><p>
      </p><p>
       Zero is returned if the column number is out of range, or if the
       specified column is not a simple reference to a table column.
      </p></dd><dt id="LIBPQ-PQFFORMAT"><span class="term"><code class="function">PQfformat</code><a id="id-1.7.3.10.4.3.7.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the format code indicating the format of the given
       column.  Column numbers start at 0.
</p><pre class="synopsis">
int PQfformat(const PGresult *res,
              int column_number);
</pre><p>
      </p><p>
       Format code zero indicates textual data representation, while format
       code one indicates binary representation.  (Other codes are reserved
       for future definition.)
      </p></dd><dt id="LIBPQ-PQFTYPE"><span class="term"><code class="function">PQftype</code><a id="id-1.7.3.10.4.3.8.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the data type associated with the given  column number.
       The  integer  returned is the internal OID number of the type.
       Column numbers start at 0.
</p><pre class="synopsis">
Oid PQftype(const PGresult *res,
            int column_number);
</pre><p>
      </p><p>
       You can query the system table <code class="literal">pg_type</code> to
       obtain the names and properties of the various data types. The
       <acronym class="acronym">OID</acronym>s of the built-in data types are defined
       in the file <code class="filename">catalog/pg_type_d.h</code>
       in the <span class="productname">PostgreSQL</span>
       installation's <code class="filename">include</code> directory.
      </p></dd><dt id="LIBPQ-PQFMOD"><span class="term"><code class="function">PQfmod</code><a id="id-1.7.3.10.4.3.9.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns  the type modifier of the column associated with the
       given column number.  Column numbers start at 0.
</p><pre class="synopsis">
int PQfmod(const PGresult *res,
           int column_number);
</pre><p>
      </p><p>
       The interpretation of modifier values is type-specific; they
       typically indicate precision or size limits.  The value -1 is
       used to indicate <span class="quote"><span class="quote">no information available</span></span>.  Most data
       types do not use modifiers, in which case the value is always
       -1.
      </p></dd><dt id="LIBPQ-PQFSIZE"><span class="term"><code class="function">PQfsize</code><a id="id-1.7.3.10.4.3.10.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns  the  size  in bytes of the column associated with the
       given column number.  Column numbers start at 0.
</p><pre class="synopsis">
int PQfsize(const PGresult *res,
            int column_number);
</pre><p>
      </p><p>
       <a class="xref" href="libpq-exec.html#LIBPQ-PQFSIZE"><code class="function">PQfsize</code></a> returns the space allocated for this column
       in a database row, in other words the size of the server's
       internal representation of the data type.  (Accordingly, it is
       not really very useful to clients.) A negative value indicates
       the data type is variable-length.
      </p></dd><dt id="LIBPQ-PQBINARYTUPLES"><span class="term"><code class="function">PQbinaryTuples</code><a id="id-1.7.3.10.4.3.11.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns 1 if the <code class="structname">PGresult</code> contains binary data
       and 0 if it contains text data.
</p><pre class="synopsis">
int PQbinaryTuples(const PGresult *res);
</pre><p>
      </p><p>
       This function is deprecated (except for its use in connection with
       <code class="command">COPY</code>), because it is possible for a single
       <code class="structname">PGresult</code> to contain text data in some columns and
       binary data in others.  <a class="xref" href="libpq-exec.html#LIBPQ-PQFFORMAT"><code class="function">PQfformat</code></a> is preferred.
       <a class="xref" href="libpq-exec.html#LIBPQ-PQBINARYTUPLES"><code class="function">PQbinaryTuples</code></a> returns 1 only if all columns of the
       result are binary (format 1).
      </p></dd><dt id="LIBPQ-PQGETVALUE"><span class="term"><code class="function">PQgetvalue</code><a id="id-1.7.3.10.4.3.12.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns a single field value of one row of a
       <code class="structname">PGresult</code>.  Row and column numbers start
       at 0.  The caller should not free the result directly.  It will
       be freed when the associated <code class="structname">PGresult</code> handle is
       passed to <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a>.
</p><pre class="synopsis">
char *PQgetvalue(const PGresult *res,
                 int row_number,
                 int column_number);
</pre><p>
      </p><p>
       For data in text format, the value returned by
       <a class="xref" href="libpq-exec.html#LIBPQ-PQGETVALUE"><code class="function">PQgetvalue</code></a> is a null-terminated character
       string  representation of the field value.  For data in binary
       format, the value is in the binary representation determined by
       the data type's <code class="function">typsend</code> and <code class="function">typreceive</code>
       functions.  (The value is actually followed by a zero byte in
       this case too, but that is not ordinarily useful, since the
       value is likely to contain embedded nulls.)
      </p><p>
       An empty string is returned if the field value is null.  See
       <a class="xref" href="libpq-exec.html#LIBPQ-PQGETISNULL"><code class="function">PQgetisnull</code></a> to distinguish null values from
       empty-string values.
      </p><p>
       The pointer returned  by  <a class="xref" href="libpq-exec.html#LIBPQ-PQGETVALUE"><code class="function">PQgetvalue</code></a> points
       to storage that is part of the <code class="structname">PGresult</code>
       structure.  One should not modify the data it points to, and one
       must explicitly copy the data into other storage if it is to be
       used past the lifetime of the  <code class="structname">PGresult</code>
       structure itself.
      </p></dd><dt id="LIBPQ-PQGETISNULL"><span class="term"><code class="function">PQgetisnull</code><a id="id-1.7.3.10.4.3.13.1.2" class="indexterm"></a><a id="id-1.7.3.10.4.3.13.1.3" class="indexterm"></a></span></dt><dd><p>
       Tests a field for a null value.  Row and column numbers start
       at 0.
</p><pre class="synopsis">
int PQgetisnull(const PGresult *res,
                int row_number,
                int column_number);
</pre><p>
      </p><p>
       This function returns  1 if the field is null and 0 if it
       contains a non-null value.  (Note that
       <a class="xref" href="libpq-exec.html#LIBPQ-PQGETVALUE"><code class="function">PQgetvalue</code></a> will return an empty string,
       not a null pointer, for a null field.)
      </p></dd><dt id="LIBPQ-PQGETLENGTH"><span class="term"><code class="function">PQgetlength</code><a id="id-1.7.3.10.4.3.14.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the actual length of a field value in bytes.  Row and
       column numbers start at 0.
</p><pre class="synopsis">
int PQgetlength(const PGresult *res,
                int row_number,
                int column_number);
</pre><p>
      </p><p>
       This is the actual data length for the particular data value,
       that is, the size of the object pointed to by
       <a class="xref" href="libpq-exec.html#LIBPQ-PQGETVALUE"><code class="function">PQgetvalue</code></a>.  For text data format this is
       the same as <code class="function">strlen()</code>.  For binary format this is
       essential information.  Note that one should <span class="emphasis"><em>not</em></span>
       rely on <a class="xref" href="libpq-exec.html#LIBPQ-PQFSIZE"><code class="function">PQfsize</code></a> to obtain the actual data
       length.
      </p></dd><dt id="LIBPQ-PQNPARAMS"><span class="term"><code class="function">PQnparams</code><a id="id-1.7.3.10.4.3.15.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the number of parameters of a prepared statement.
</p><pre class="synopsis">
int PQnparams(const PGresult *res);
</pre><p>
      </p><p>
       This function is only useful when inspecting the result of
       <a class="xref" href="libpq-exec.html#LIBPQ-PQDESCRIBEPREPARED"><code class="function">PQdescribePrepared</code></a>.  For other types of queries it
       will return zero.
      </p></dd><dt id="LIBPQ-PQPARAMTYPE"><span class="term"><code class="function">PQparamtype</code><a id="id-1.7.3.10.4.3.16.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the data type of the indicated statement parameter.
       Parameter numbers start at 0.
</p><pre class="synopsis">
Oid PQparamtype(const PGresult *res, int param_number);
</pre><p>
      </p><p>
       This function is only useful when inspecting the result of
       <a class="xref" href="libpq-exec.html#LIBPQ-PQDESCRIBEPREPARED"><code class="function">PQdescribePrepared</code></a>.  For other types of queries it
       will return zero.
      </p></dd><dt id="LIBPQ-PQPRINT"><span class="term"><code class="function">PQprint</code><a id="id-1.7.3.10.4.3.17.1.2" class="indexterm"></a></span></dt><dd><p>
       Prints out all the rows and,  optionally,  the column names  to
       the specified output stream.
</p><pre class="synopsis">
void PQprint(FILE *fout,      /* output stream */
             const PGresult *res,
             const PQprintOpt *po);
typedef struct
{
    pqbool  header;      /* print output field headings and row count */
    pqbool  align;       /* fill align the fields */
    pqbool  standard;    /* old brain dead format */
    pqbool  html3;       /* output HTML tables */
    pqbool  expanded;    /* expand tables */
    pqbool  pager;       /* use pager for output if needed */
    char    *fieldSep;   /* field separator */
    char    *tableOpt;   /* attributes for HTML table element */
    char    *caption;    /* HTML table caption */
    char    **fieldName; /* null-terminated array of replacement field names */
} PQprintOpt;
</pre><p>
      </p><p>
       This function was formerly used by <span class="application">psql</span>
       to print query results, but this is no longer the case.  Note
       that it assumes all the data is in text format.
      </p></dd></dl></div></div><div class="sect2" id="LIBPQ-EXEC-NONSELECT"><div class="titlepage"><div><div><h3 class="title">34.3.3. Retrieving Other Result Information</h3></div></div></div><p>
    These functions are used to extract other information from
    <code class="structname">PGresult</code> objects.
   </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQCMDSTATUS"><span class="term"><code class="function">PQcmdStatus</code><a id="id-1.7.3.10.5.3.1.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the command status tag from the SQL command that generated
       the <code class="structname">PGresult</code>.
</p><pre class="synopsis">
char *PQcmdStatus(PGresult *res);
</pre><p>
      </p><p>
       Commonly this is just the name of the command, but it might include
       additional data such as the number of rows processed. The caller
       should not free the result directly. It will be freed when the
       associated <code class="structname">PGresult</code> handle is passed to
       <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a>.
      </p></dd><dt id="LIBPQ-PQCMDTUPLES"><span class="term"><code class="function">PQcmdTuples</code><a id="id-1.7.3.10.5.3.2.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the number of rows affected by the SQL command.
</p><pre class="synopsis">
char *PQcmdTuples(PGresult *res);
</pre><p>
      </p><p>
       This function returns a string containing the number of rows
       affected by the <acronym class="acronym">SQL</acronym> statement that generated the
       <code class="structname">PGresult</code>. This function can only be used following
       the execution of a <code class="command">SELECT</code>, <code class="command">CREATE TABLE AS</code>,
       <code class="command">INSERT</code>, <code class="command">UPDATE</code>, <code class="command">DELETE</code>,
       <code class="command">MERGE</code>, <code class="command">MOVE</code>, <code class="command">FETCH</code>,
       or <code class="command">COPY</code> statement, or an <code class="command">EXECUTE</code> of a
       prepared query that contains an <code class="command">INSERT</code>,
       <code class="command">UPDATE</code>, <code class="command">DELETE</code>,
       or <code class="command">MERGE</code> statement.
       If the command that generated the <code class="structname">PGresult</code> was anything
       else, <a class="xref" href="libpq-exec.html#LIBPQ-PQCMDTUPLES"><code class="function">PQcmdTuples</code></a> returns an empty string. The caller
       should not free the return value directly. It will be freed when
       the associated <code class="structname">PGresult</code> handle is passed to
       <a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a>.
      </p></dd><dt id="LIBPQ-PQOIDVALUE"><span class="term"><code class="function">PQoidValue</code><a id="id-1.7.3.10.5.3.3.1.2" class="indexterm"></a></span></dt><dd><p>
       Returns the OID<a id="id-1.7.3.10.5.3.3.2.1.1" class="indexterm"></a>
       of the inserted row, if the <acronym class="acronym">SQL</acronym> command was an
       <code class="command">INSERT</code> that inserted exactly one row into a table that
       has OIDs, or a <code class="command">EXECUTE</code> of a prepared query containing
       a suitable <code class="command">INSERT</code> statement.  Otherwise, this function
       returns <code class="literal">InvalidOid</code>. This function will also
       return <code class="literal">InvalidOid</code> if the table affected by the
       <code class="command">INSERT</code> statement does not contain OIDs.
</p><pre class="synopsis">
Oid PQoidValue(const PGresult *res);
</pre><p>
      </p></dd><dt id="LIBPQ-PQOIDSTATUS"><span class="term"><code class="function">PQoidStatus</code><a id="id-1.7.3.10.5.3.4.1.2" class="indexterm"></a></span></dt><dd><p>
       This function is deprecated in favor of
       <a class="xref" href="libpq-exec.html#LIBPQ-PQOIDVALUE"><code class="function">PQoidValue</code></a> and is not thread-safe.
       It returns a string with the OID of the inserted row, while
       <a class="xref" href="libpq-exec.html#LIBPQ-PQOIDVALUE"><code class="function">PQoidValue</code></a> returns the OID value.
</p><pre class="synopsis">
char *PQoidStatus(const PGresult *res);
</pre><p>
      </p></dd></dl></div></div><div class="sect2" id="LIBPQ-EXEC-ESCAPE-STRING"><div class="titlepage"><div><div><h3 class="title">34.3.4. Escaping Strings for Inclusion in SQL Commands</h3></div></div></div><a id="id-1.7.3.10.6.2" class="indexterm"></a><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQESCAPELITERAL"><span class="term"><code class="function">PQescapeLiteral</code><a id="id-1.7.3.10.6.3.1.1.2" class="indexterm"></a></span></dt><dd><p>
</p><pre class="synopsis">
char *PQescapeLiteral(PGconn *conn, const char *str, size_t length);
</pre><p>
     </p><p>
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPELITERAL"><code class="function">PQescapeLiteral</code></a> escapes a string for
      use within an SQL command.  This is useful when inserting data
      values as literal constants in SQL commands.  Certain characters
      (such as quotes and backslashes) must be escaped to prevent them
      from being interpreted specially by the SQL parser.
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPELITERAL"><code class="function">PQescapeLiteral</code></a> performs this operation.
     </p><p>
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPELITERAL"><code class="function">PQescapeLiteral</code></a> returns an escaped version of the
      <em class="parameter"><code>str</code></em> parameter in memory allocated with
      <code class="function">malloc()</code>.  This memory should be freed using
      <code class="function">PQfreemem()</code> when the result is no longer needed.
      A terminating zero byte is not required, and should not be
      counted in <em class="parameter"><code>length</code></em>.  (If a terminating zero byte is found
      before <em class="parameter"><code>length</code></em> bytes are processed,
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPELITERAL"><code class="function">PQescapeLiteral</code></a> stops at the zero; the behavior is
      thus rather like <code class="function">strncpy</code>.) The
      return string has all special characters replaced so that they can
      be properly processed by the <span class="productname">PostgreSQL</span>
      string literal parser.  A terminating zero byte is also added.  The
      single quotes that must surround <span class="productname">PostgreSQL</span>
      string literals are included in the result string.
     </p><p>
      On error, <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPELITERAL"><code class="function">PQescapeLiteral</code></a> returns <code class="symbol">NULL</code> and a suitable
      message is stored in the <em class="parameter"><code>conn</code></em> object.
     </p><div class="tip"><h3 class="title">Tip</h3><p>
       It is especially important to do proper escaping when handling
       strings that were received from an untrustworthy source.
       Otherwise there is a security risk: you are vulnerable to
       <span class="quote"><span class="quote">SQL injection</span></span> attacks wherein unwanted SQL commands are
       fed to your database.
      </p></div><p>
      Note that it is neither necessary nor correct to do escaping when a data
      value is passed as a separate parameter in <a class="xref" href="libpq-exec.html#LIBPQ-PQEXECPARAMS"><code class="function">PQexecParams</code></a> or
      its sibling routines.
     </p></dd><dt id="LIBPQ-PQESCAPEIDENTIFIER"><span class="term"><code class="function">PQescapeIdentifier</code><a id="id-1.7.3.10.6.3.2.1.2" class="indexterm"></a></span></dt><dd><p>
</p><pre class="synopsis">
char *PQescapeIdentifier(PGconn *conn, const char *str, size_t length);
</pre><p>
     </p><p>
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEIDENTIFIER"><code class="function">PQescapeIdentifier</code></a> escapes a string for
      use as an SQL identifier, such as a table, column, or function name.
      This is useful when a user-supplied identifier might contain
      special characters that would otherwise not be interpreted as part
      of the identifier by the SQL parser, or when the identifier might
      contain upper case characters whose case should be preserved.
     </p><p>
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEIDENTIFIER"><code class="function">PQescapeIdentifier</code></a> returns a version of the
      <em class="parameter"><code>str</code></em> parameter escaped as an SQL identifier
      in memory allocated with <code class="function">malloc()</code>.  This memory must be
      freed using <code class="function">PQfreemem()</code> when the result is no longer
      needed.  A terminating zero byte is not required, and should not be
      counted in <em class="parameter"><code>length</code></em>.  (If a terminating zero byte is found
      before <em class="parameter"><code>length</code></em> bytes are processed,
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEIDENTIFIER"><code class="function">PQescapeIdentifier</code></a> stops at the zero; the behavior is
      thus rather like <code class="function">strncpy</code>.) The
      return string has all special characters replaced so that it
      will be properly processed as an SQL identifier.  A terminating zero byte
      is also added.  The return string will also be surrounded by double
      quotes.
     </p><p>
      On error, <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEIDENTIFIER"><code class="function">PQescapeIdentifier</code></a> returns <code class="symbol">NULL</code> and a suitable
      message is stored in the <em class="parameter"><code>conn</code></em> object.
     </p><div class="tip"><h3 class="title">Tip</h3><p>
       As with string literals, to prevent SQL injection attacks,
       SQL identifiers must be escaped when they are received from an
       untrustworthy source.
      </p></div></dd><dt id="LIBPQ-PQESCAPESTRINGCONN"><span class="term"><code class="function">PQescapeStringConn</code><a id="id-1.7.3.10.6.3.3.1.2" class="indexterm"></a></span></dt><dd><p>
</p><pre class="synopsis">
size_t PQescapeStringConn(PGconn *conn,
                          char *to, const char *from, size_t length,
                          int *error);
</pre><p>
     </p><p>
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRINGCONN"><code class="function">PQescapeStringConn</code></a> escapes string literals, much like
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPELITERAL"><code class="function">PQescapeLiteral</code></a>.  Unlike <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPELITERAL"><code class="function">PQescapeLiteral</code></a>,
      the caller is responsible for providing an appropriately sized buffer.
      Furthermore, <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRINGCONN"><code class="function">PQescapeStringConn</code></a> does not generate the
      single quotes that must surround <span class="productname">PostgreSQL</span> string
      literals; they should be provided in the SQL command that the
      result is inserted into.  The parameter <em class="parameter"><code>from</code></em> points to
      the first character of the string that is to be escaped, and the
      <em class="parameter"><code>length</code></em> parameter gives the number of bytes in this
      string.  A terminating zero byte is not required, and should not be
      counted in <em class="parameter"><code>length</code></em>.  (If a terminating zero byte is found
      before <em class="parameter"><code>length</code></em> bytes are processed,
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRINGCONN"><code class="function">PQescapeStringConn</code></a> stops at the zero; the behavior is
      thus rather like <code class="function">strncpy</code>.) <em class="parameter"><code>to</code></em> shall point
      to a buffer that is able to hold at least one more byte than twice
      the value of <em class="parameter"><code>length</code></em>, otherwise the behavior is undefined.
      Behavior is likewise undefined if the <em class="parameter"><code>to</code></em> and
      <em class="parameter"><code>from</code></em> strings overlap.
     </p><p>
      If the <em class="parameter"><code>error</code></em> parameter is not <code class="symbol">NULL</code>, then
      <code class="literal">*error</code> is set to zero on success, nonzero on error.
      Presently the only possible error conditions involve invalid multibyte
      encoding in the source string.  The output string is still generated
      on error, but it can be expected that the server will reject it as
      malformed.  On error, a suitable message is stored in the
      <em class="parameter"><code>conn</code></em> object, whether or not <em class="parameter"><code>error</code></em> is <code class="symbol">NULL</code>.
     </p><p>
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRINGCONN"><code class="function">PQescapeStringConn</code></a> returns the number of bytes written
      to <em class="parameter"><code>to</code></em>, not including the terminating zero byte.
     </p></dd><dt id="LIBPQ-PQESCAPESTRING"><span class="term"><code class="function">PQescapeString</code><a id="id-1.7.3.10.6.3.4.1.2" class="indexterm"></a></span></dt><dd><p>
       <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRING"><code class="function">PQescapeString</code></a> is an older, deprecated version of
       <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRINGCONN"><code class="function">PQescapeStringConn</code></a>.
</p><pre class="synopsis">
size_t PQescapeString (char *to, const char *from, size_t length);
</pre><p>
     </p><p>
      The only difference from <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRINGCONN"><code class="function">PQescapeStringConn</code></a> is that
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRING"><code class="function">PQescapeString</code></a> does not take <code class="structname">PGconn</code>
      or <em class="parameter"><code>error</code></em> parameters.
      Because of this, it cannot adjust its behavior depending on the
      connection properties (such as character encoding) and therefore
      <span class="emphasis"><em>it might give the wrong results</em></span>.  Also, it has no way
      to report error conditions.
     </p><p>
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRING"><code class="function">PQescapeString</code></a> can be used safely in
      client programs that work with only one <span class="productname">PostgreSQL</span>
      connection at a time (in this case it can find out what it needs to
      know <span class="quote"><span class="quote">behind the scenes</span></span>).  In other contexts it is a security
      hazard and should be avoided in favor of
      <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRINGCONN"><code class="function">PQescapeStringConn</code></a>.
     </p></dd><dt id="LIBPQ-PQESCAPEBYTEACONN"><span class="term"><code class="function">PQescapeByteaConn</code><a id="id-1.7.3.10.6.3.5.1.2" class="indexterm"></a></span></dt><dd><p>
       Escapes binary data for use within an SQL command with the type
       <code class="type">bytea</code>.  As with <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPESTRINGCONN"><code class="function">PQescapeStringConn</code></a>,
       this is only used when inserting data directly into an SQL command string.
</p><pre class="synopsis">
unsigned char *PQescapeByteaConn(PGconn *conn,
                                 const unsigned char *from,
                                 size_t from_length,
                                 size_t *to_length);
</pre><p>
      </p><p>
       Certain byte values must be escaped when used as part of a
       <code class="type">bytea</code> literal in an <acronym class="acronym">SQL</acronym> statement.
       <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEACONN"><code class="function">PQescapeByteaConn</code></a> escapes bytes using
       either hex encoding or backslash escaping.  See <a class="xref" href="datatype-binary.html" title="8.4. Binary Data Types">Section 8.4</a> for more information.
      </p><p>
       The <em class="parameter"><code>from</code></em> parameter points to the first
       byte of the string that is to be escaped, and the
       <em class="parameter"><code>from_length</code></em> parameter gives the number of
       bytes in this binary string.  (A terminating zero byte is
       neither necessary nor counted.)  The <em class="parameter"><code>to_length</code></em>
       parameter points to a variable that will hold the resultant
       escaped string length. This result string length includes the terminating
       zero byte of the result.
      </p><p>
       <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEACONN"><code class="function">PQescapeByteaConn</code></a> returns an escaped version of the
       <em class="parameter"><code>from</code></em> parameter binary string in memory
       allocated with <code class="function">malloc()</code>.  This memory should be freed using
       <code class="function">PQfreemem()</code> when the result is no longer needed.  The
       return string has all special characters replaced so that they can
       be properly processed by the <span class="productname">PostgreSQL</span>
       string literal parser, and the <code class="type">bytea</code> input function. A
       terminating zero byte is also added.  The single quotes that must
       surround <span class="productname">PostgreSQL</span> string literals are
       not part of the result string.
      </p><p>
       On error, a null pointer is returned, and a suitable error message
       is stored in the <em class="parameter"><code>conn</code></em> object.  Currently, the only
       possible error is insufficient memory for the result string.
      </p></dd><dt id="LIBPQ-PQESCAPEBYTEA"><span class="term"><code class="function">PQescapeBytea</code><a id="id-1.7.3.10.6.3.6.1.2" class="indexterm"></a></span></dt><dd><p>
       <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEA"><code class="function">PQescapeBytea</code></a> is an older, deprecated version of
       <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEACONN"><code class="function">PQescapeByteaConn</code></a>.
</p><pre class="synopsis">
unsigned char *PQescapeBytea(const unsigned char *from,
                             size_t from_length,
                             size_t *to_length);
</pre><p>
      </p><p>
       The only difference from <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEACONN"><code class="function">PQescapeByteaConn</code></a> is that
       <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEA"><code class="function">PQescapeBytea</code></a> does not take a <code class="structname">PGconn</code>
       parameter.  Because of this, <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEA"><code class="function">PQescapeBytea</code></a> can
       only be used safely in client programs that use a single
       <span class="productname">PostgreSQL</span> connection at a time (in this case
       it can find out what it needs to know <span class="quote"><span class="quote">behind the
       scenes</span></span>).  It <span class="emphasis"><em>might give the wrong results</em></span> if
       used in programs that use multiple database connections (use
       <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEACONN"><code class="function">PQescapeByteaConn</code></a> in such cases).
      </p></dd><dt id="LIBPQ-PQUNESCAPEBYTEA"><span class="term"><code class="function">PQunescapeBytea</code><a id="id-1.7.3.10.6.3.7.1.2" class="indexterm"></a></span></dt><dd><p>
       Converts a string representation of binary data into binary data
       — the reverse of <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEA"><code class="function">PQescapeBytea</code></a>.  This
       is needed when retrieving <code class="type">bytea</code> data in text format,
       but not when retrieving it in binary format.

</p><pre class="synopsis">
unsigned char *PQunescapeBytea(const unsigned char *from, size_t *to_length);
</pre><p>
      </p><p>
       The <em class="parameter"><code>from</code></em> parameter points to a string
       such as might be returned by <a class="xref" href="libpq-exec.html#LIBPQ-PQGETVALUE"><code class="function">PQgetvalue</code></a> when applied
       to a <code class="type">bytea</code> column. <a class="xref" href="libpq-exec.html#LIBPQ-PQUNESCAPEBYTEA"><code class="function">PQunescapeBytea</code></a>
       converts this string representation into its binary representation.
       It returns a pointer to a buffer allocated with
       <code class="function">malloc()</code>, or <code class="symbol">NULL</code> on error, and puts the size of
       the buffer in <em class="parameter"><code>to_length</code></em>. The result must be
       freed using <a class="xref" href="libpq-misc.html#LIBPQ-PQFREEMEM"><code class="function">PQfreemem</code></a> when it is no longer needed.
      </p><p>
       This conversion is not exactly the inverse of
       <a class="xref" href="libpq-exec.html#LIBPQ-PQESCAPEBYTEA"><code class="function">PQescapeBytea</code></a>, because the string is not expected
       to be <span class="quote"><span class="quote">escaped</span></span> when received from <a class="xref" href="libpq-exec.html#LIBPQ-PQGETVALUE"><code class="function">PQgetvalue</code></a>.
       In particular this means there is no need for string quoting considerations,
       and so no need for a <code class="structname">PGconn</code> parameter.
      </p></dd></dl></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="libpq-status.html" title="34.2. Connection Status Functions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="libpq.html" title="Chapter 34. libpq — C Library">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="libpq-async.html" title="34.4. Asynchronous Command Processing">Next</a></td></tr><tr><td width="40%" align="left" valign="top">34.2. Connection Status Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.6 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 34.4. Asynchronous Command Processing</td></tr></table></div></body></html>