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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-13 14:07:11 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-13 14:07:11 +0000
commit63847496f14c813a5d80efd5b7de0f1294ffe1e3 (patch)
tree01c7571c7c762ceee70638549a99834fdd7c411b /www/stmt.html
parentInitial commit. (diff)
downloadsqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.tar.xz
sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.zip
Adding upstream version 3.45.1.upstream/3.45.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<!DOCTYPE html>
+<html><head>
+<meta name="viewport" content="width=device-width, initial-scale=1.0">
+<meta http-equiv="content-type" content="text/html; charset=UTF-8">
+<link href="sqlite.css" rel="stylesheet">
+<title>The SQLITE_STMT Virtual Table</title>
+<!-- path= -->
+</head>
+<body>
+<div class=nosearch>
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+<div class=fancy>
+<div class=nosearch>
+<div class="fancy_title">
+The SQLITE_STMT Virtual Table
+</div>
+</div>
+
+
+
+
+<h1 id="overview"><span>1. </span>Overview</h1>
+
+<p>
+The SQLITE_STMT extension implements an <a href="vtab.html#epoonlyvtab">eponymous-only virtual table</a> that
+provides information about all <a href="c3ref/stmt.html">prepared statements</a> associated with
+the <a href="c3ref/sqlite3.html">database connection</a>.
+</p>
+
+<p>
+The SQLITE_STMT extension is included in the <a href="amalgamation.html">amalgamation</a> though
+it is disabled
+by default. Use the <a href="compile.html#enable_stmtvtab">SQLITE_ENABLE_STMTVTAB</a> compile-time option to enable
+the SQLITE_STMT extension. The SQLITE_STMT extension can also be
+loaded at run-time
+by compiling the extension into a shared library or DLL using the source
+code at <a href="https://sqlite.org/src/file/ext/misc/stmt.c">https://sqlite.org/src/file/ext/misc/stmt.c</a> and following the
+instructions for how to <a href="loadext.html#build">compile loadable extensions</a>.
+</p>
+
+<p>
+The SQLITE_STMT extension is enabled in default builds
+of the <a href="cli.html">command-line shell</a>.
+
+</p><h1 id="usage"><span>2. </span>Usage</h1>
+
+<p>
+The SQLITE_STMT virtual table is a read-only table that can be directly
+queried to access information about all prepared statements on the
+current database connection. For example:
+
+</p><div class="codeblock"><pre>SELECT * FROM sqlite_stmt;
+</pre></div>
+
+<p>
+A statement such as the above can be run immediately prior to invoking
+<a href="c3ref/close.html">sqlite3_close()</a> to confirm that all prepared statements have been
+<a href="c3ref/finalize.html">finalized</a> and to help identify and track down prepared
+statements that have "leaked" and missed finalization.
+
+</p><p>
+The SQLITE_STMT virtual table can also be used to access performance
+information about prepared statements, to aid in optimization an application.
+For example,
+to find out how much memory is being used by <a href="c3ref/stmt.html">prepared statements</a> that have
+never been used, one could run:
+
+</p><div class="codeblock"><pre>SELECT sum(mem) FROM sqlite_stmt WHERE run=0;
+</pre></div>
+
+<h2 id="columns"><span>2.1. </span>Columns</h2>
+
+<p>
+The columns are provided by the SQLITE_STMT virtual table are summarized by
+the hypothetical CREATE TABLE statement show here:
+
+</p><div class="codeblock"><pre>CREATE TABLE sqlite_stmt(
+ sql TEXT, -- Original SQL text
+ ncol INT, -- Number of output columns
+ ro BOOLEAN, -- True for "read only" statements
+ busy BOOLEAN, -- True if the statement is current running
+ nscan INT, -- Number of full-scan steps
+ nsort INT, -- Number of sort operations
+ naidx INT, -- Number of automatic index inserts
+ nstep INT, -- Number of byte-code engine steps
+ reprep INT, -- Number of reprepare operations
+ run INT, -- Number of times this statement has been run
+ mem INT -- Heap memory used by this statement
+);
+</pre></div>
+
+<p>Future releases may add new output columns and may change the order
+of legacy columns.
+Further detail about the meaning of each column in the SQLITE_STMT virtual
+table is provided below:
+
+</p><ul>
+<li><p><b>sql</b>:
+The original SQL text of the prepared statement. If the prepared
+statement is compiled using the <a href="c3ref/prepare.html">sqlite3_prepare()</a> interface, then
+the SQL text might not have been saved, in which case this column
+will be NULL.
+
+</p></li><li><p><b>ncol</b>:
+The number of columns in the result set of a query.
+For DML statements, this column has a value of 0.
+
+</p></li><li><p><b>ro</b>:
+The "read only" column. This column is true (non-zero) if the
+SQL statement is a query and false (zero) if it is a DML statement.
+
+</p></li><li><p><b>busy</b>:
+This field is true if the prepared statement is currently running.
+In other words, this field is true if <a href="c3ref/step.html">sqlite3_step()</a> has been called
+on the <a href="c3ref/stmt.html">prepared statement</a> at least once but <a href="c3ref/reset.html">sqlite3_reset()</a> has
+not yet been called to reset it.
+
+</p></li><li><p><b>nscan</b>:
+This field is the number of times that the <a href="opcode.html">bytecode engine</a> has stepped
+through a table as part of a full-table scan. A large number if this
+field may indicate an opportunity to improve performance by adding an
+index. This field is equivalent to the <a href="c3ref/c_stmtstatus_counter.html#sqlitestmtstatusfullscanstep">SQLITE_STMTSTATUS_FULLSCAN_STEP</a>
+value.
+
+</p></li><li><p><b>nsort</b>:
+This field is the number of times that the <a href="opcode.html">bytecode engine</a> had to sort.
+A positive value in this field may indicate an opportunity to improve
+performance by adding an index that will cause the query results to
+appear naturally in the desired order.
+This field is equivalent to the <a href="c3ref/c_stmtstatus_counter.html#sqlitestmtstatussort">SQLITE_STMTSTATUS_SORT</a> value.
+
+</p></li><li><p><b>naidx</b>:
+This field is the number of rows that have been inserted into
+<a href="optoverview.html#autoindex">automatic indexes</a>. A positive value in this field may indicate
+an opportunity to improve performance by adding a named index that
+take the place of the automatic index.
+This field is equivalent to the <a href="c3ref/c_stmtstatus_counter.html#sqlitestmtstatusautoindex">SQLITE_STMTSTATUS_AUTOINDEX</a> value.
+
+</p></li><li><p><b>nstep</b>:
+This field is the number of <a href="opcode.html">bytecode engine</a> operations that have
+been performed for the prepared statement. This field can be used
+as a proxy for how much CPU time a statement has used.
+This field is equivalent to the <a href="c3ref/c_stmtstatus_counter.html#sqlitestmtstatusvmstep">SQLITE_STMTSTATUS_VM_STEP</a> value.
+
+</p></li><li><p><b>reprep</b>:
+This field is the number of times that the statement has had to be
+reprepared due to schema changes or changes to parameter bindings.
+This field is equivalent to the <a href="c3ref/c_stmtstatus_counter.html#sqlitestmtstatusreprepare">SQLITE_STMTSTATUS_REPREPARE</a> value.
+
+</p></li><li><p><b>run</b>:
+This field is the number of times that the statement has been run.
+This field is equivalent to the <a href="c3ref/c_stmtstatus_counter.html#sqlitestmtstatusrun">SQLITE_STMTSTATUS_RUN</a> value.
+
+</p></li><li><p><b>mem</b>:
+This field is the number of bytes of heap storage used by the
+prepared statement.
+This field is equivalent to the <a href="c3ref/c_stmtstatus_counter.html#sqlitestmtstatusmemused">SQLITE_STMTSTATUS_MEMUSED</a> value.
+</p></li></ul>
+<p align="center"><small><i>This page last modified on <a href="https://sqlite.org/docsrc/honeypot" id="mtimelink" data-href="https://sqlite.org/docsrc/finfo/pages/stmt.in?m=9368174a6e">2022-01-08 05:02:57</a> UTC </small></i></p>
+
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