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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>9.2. Comparison Functions and Operators</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="functions-logical.html" title="9.1. Logical Operators" /><link rel="next" href="functions-math.html" title="9.3. Mathematical Functions and Operators" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.2. Comparison Functions and Operators</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-logical.html" title="9.1. Logical Operators">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><th width="60%" align="center">Chapter 9. Functions and Operators</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-math.html" title="9.3. Mathematical Functions and Operators">Next</a></td></tr></table><hr /></div><div class="sect1" id="FUNCTIONS-COMPARISON"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.2. Comparison Functions and Operators</h2></div></div></div><a id="id-1.5.8.8.2" class="indexterm"></a><p>
    The usual comparison operators are available, as shown in <a class="xref" href="functions-comparison.html#FUNCTIONS-COMPARISON-OP-TABLE" title="Table 9.1. Comparison Operators">Table 9.1</a>.
   </p><div class="table" id="FUNCTIONS-COMPARISON-OP-TABLE"><p class="title"><strong>Table 9.1. Comparison Operators</strong></p><div class="table-contents"><table class="table" summary="Comparison Operators" border="1"><colgroup><col /><col /></colgroup><thead><tr><th>Operator</th><th>Description</th></tr></thead><tbody><tr><td>
        <em class="replaceable"><code>datatype</code></em> <code class="literal">&lt;</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </td><td>Less than</td></tr><tr><td>
        <em class="replaceable"><code>datatype</code></em> <code class="literal">&gt;</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </td><td>Greater than</td></tr><tr><td>
        <em class="replaceable"><code>datatype</code></em> <code class="literal">&lt;=</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </td><td>Less than or equal to</td></tr><tr><td>
        <em class="replaceable"><code>datatype</code></em> <code class="literal">&gt;=</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </td><td>Greater than or equal to</td></tr><tr><td>
        <em class="replaceable"><code>datatype</code></em> <code class="literal">=</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </td><td>Equal</td></tr><tr><td>
        <em class="replaceable"><code>datatype</code></em> <code class="literal">&lt;&gt;</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </td><td>Not equal</td></tr><tr><td>
        <em class="replaceable"><code>datatype</code></em> <code class="literal">!=</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </td><td>Not equal</td></tr></tbody></table></div></div><br class="table-break" /><div class="note"><h3 class="title">Note</h3><p>
     <code class="literal">&lt;&gt;</code> is the standard SQL notation for <span class="quote"><span class="quote">not
     equal</span></span>.  <code class="literal">!=</code> is an alias, which is converted
     to <code class="literal">&lt;&gt;</code> at a very early stage of parsing.
     Hence, it is not possible to implement <code class="literal">!=</code>
     and <code class="literal">&lt;&gt;</code> operators that do different things.
    </p></div><p>
    These comparison operators are available for all built-in data types
    that have a natural ordering, including numeric, string, and date/time
    types.  In addition, arrays, composite types, and ranges can be compared
    if their component data types are comparable.
   </p><p>
    It is usually possible to compare values of related data
    types as well; for example <code class="type">integer</code> <code class="literal">&gt;</code>
    <code class="type">bigint</code> will work.  Some cases of this sort are implemented
    directly by <span class="quote"><span class="quote">cross-type</span></span> comparison operators, but if no
    such operator is available, the parser will coerce the less-general type
    to the more-general type and apply the latter's comparison operator.
   </p><p>
    As shown above, all comparison operators are binary operators that
    return values of type <code class="type">boolean</code>.  Thus, expressions like
    <code class="literal">1 &lt; 2 &lt; 3</code> are not valid (because there is
    no <code class="literal">&lt;</code> operator to compare a Boolean value with
    <code class="literal">3</code>).  Use the <code class="literal">BETWEEN</code> predicates
    shown below to perform range tests.
   </p><p>
    There are also some comparison predicates, as shown in <a class="xref" href="functions-comparison.html#FUNCTIONS-COMPARISON-PRED-TABLE" title="Table 9.2. Comparison Predicates">Table 9.2</a>.  These behave much like
    operators, but have special syntax mandated by the SQL standard.
   </p><div class="table" id="FUNCTIONS-COMPARISON-PRED-TABLE"><p class="title"><strong>Table 9.2. Comparison Predicates</strong></p><div class="table-contents"><table class="table" summary="Comparison Predicates" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
        Predicate
       </p>
       <p>
        Description
       </p>
       <p>
        Example(s)
       </p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">BETWEEN</code> <em class="replaceable"><code>datatype</code></em> <code class="literal">AND</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </p>
       <p>
        Between (inclusive of the range endpoints).
       </p>
       <p>
        <code class="literal">2 BETWEEN 1 AND 3</code><code class="returnvalue">t</code>
       </p>
       <p>
        <code class="literal">2 BETWEEN 3 AND 1</code><code class="returnvalue">f</code>
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">NOT BETWEEN</code> <em class="replaceable"><code>datatype</code></em> <code class="literal">AND</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </p>
       <p>
        Not between (the negation of <code class="literal">BETWEEN</code>).
       </p>
       <p>
        <code class="literal">2 NOT BETWEEN 1 AND 3</code><code class="returnvalue">f</code>
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">BETWEEN SYMMETRIC</code> <em class="replaceable"><code>datatype</code></em> <code class="literal">AND</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </p>
       <p>
        Between, after sorting the two endpoint values.
       </p>
       <p>
        <code class="literal">2 BETWEEN SYMMETRIC 3 AND 1</code><code class="returnvalue">t</code>
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">NOT BETWEEN SYMMETRIC</code> <em class="replaceable"><code>datatype</code></em> <code class="literal">AND</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </p>
       <p>
        Not between, after sorting the two endpoint values.
       </p>
       <p>
        <code class="literal">2 NOT BETWEEN SYMMETRIC 3 AND 1</code><code class="returnvalue">f</code>
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">IS DISTINCT FROM</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </p>
       <p>
        Not equal, treating null as a comparable value.
       </p>
       <p>
        <code class="literal">1 IS DISTINCT FROM NULL</code><code class="returnvalue">t</code> (rather than <code class="literal">NULL</code>)
       </p>
       <p>
        <code class="literal">NULL IS DISTINCT FROM NULL</code><code class="returnvalue">f</code> (rather than <code class="literal">NULL</code>)
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">IS NOT DISTINCT FROM</code> <em class="replaceable"><code>datatype</code></em><code class="returnvalue">boolean</code>
       </p>
       <p>
        Equal, treating null as a comparable value.
       </p>
       <p>
        <code class="literal">1 IS NOT DISTINCT FROM NULL</code><code class="returnvalue">f</code> (rather than <code class="literal">NULL</code>)
       </p>
       <p>
        <code class="literal">NULL IS NOT DISTINCT FROM NULL</code><code class="returnvalue">t</code> (rather than <code class="literal">NULL</code>)
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">IS NULL</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether value is null.
       </p>
       <p>
        <code class="literal">1.5 IS NULL</code><code class="returnvalue">f</code>
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">IS NOT NULL</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether value is not null.
       </p>
       <p>
        <code class="literal">'null' IS NOT NULL</code><code class="returnvalue">t</code>
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">ISNULL</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether value is null (nonstandard syntax).
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <em class="replaceable"><code>datatype</code></em> <code class="literal">NOTNULL</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether value is not null (nonstandard syntax).
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <code class="type">boolean</code> <code class="literal">IS TRUE</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether boolean expression yields true.
       </p>
       <p>
        <code class="literal">true IS TRUE</code><code class="returnvalue">t</code>
       </p>
       <p>
        <code class="literal">NULL::boolean IS TRUE</code><code class="returnvalue">f</code> (rather than <code class="literal">NULL</code>)
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <code class="type">boolean</code> <code class="literal">IS NOT TRUE</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether boolean expression yields false or unknown.
       </p>
       <p>
        <code class="literal">true IS NOT TRUE</code><code class="returnvalue">f</code>
       </p>
       <p>
        <code class="literal">NULL::boolean IS NOT TRUE</code><code class="returnvalue">t</code> (rather than <code class="literal">NULL</code>)
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <code class="type">boolean</code> <code class="literal">IS FALSE</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether boolean expression yields false.
       </p>
       <p>
        <code class="literal">true IS FALSE</code><code class="returnvalue">f</code>
       </p>
       <p>
        <code class="literal">NULL::boolean IS FALSE</code><code class="returnvalue">f</code> (rather than <code class="literal">NULL</code>)
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <code class="type">boolean</code> <code class="literal">IS NOT FALSE</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether boolean expression yields true or unknown.
       </p>
       <p>
        <code class="literal">true IS NOT FALSE</code><code class="returnvalue">t</code>
       </p>
       <p>
        <code class="literal">NULL::boolean IS NOT FALSE</code><code class="returnvalue">t</code> (rather than <code class="literal">NULL</code>)
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <code class="type">boolean</code> <code class="literal">IS UNKNOWN</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether boolean expression yields unknown.
       </p>
       <p>
        <code class="literal">true IS UNKNOWN</code><code class="returnvalue">f</code>
       </p>
       <p>
        <code class="literal">NULL::boolean IS UNKNOWN</code><code class="returnvalue">t</code> (rather than <code class="literal">NULL</code>)
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <code class="type">boolean</code> <code class="literal">IS NOT UNKNOWN</code><code class="returnvalue">boolean</code>
       </p>
       <p>
        Test whether boolean expression yields true or false.
       </p>
       <p>
        <code class="literal">true IS NOT UNKNOWN</code><code class="returnvalue">t</code>
       </p>
       <p>
        <code class="literal">NULL::boolean IS NOT UNKNOWN</code><code class="returnvalue">f</code> (rather than <code class="literal">NULL</code>)
       </p></td></tr></tbody></table></div></div><br class="table-break" /><p>
    <a id="id-1.5.8.8.11.1" class="indexterm"></a>
    <a id="id-1.5.8.8.11.2" class="indexterm"></a>
    The <code class="token">BETWEEN</code> predicate simplifies range tests:
</p><pre class="synopsis">
<em class="replaceable"><code>a</code></em> BETWEEN <em class="replaceable"><code>x</code></em> AND <em class="replaceable"><code>y</code></em>
</pre><p>
    is equivalent to
</p><pre class="synopsis">
<em class="replaceable"><code>a</code></em> &gt;= <em class="replaceable"><code>x</code></em> AND <em class="replaceable"><code>a</code></em> &lt;= <em class="replaceable"><code>y</code></em>
</pre><p>
    Notice that <code class="token">BETWEEN</code> treats the endpoint values as included
    in the range.
    <code class="literal">BETWEEN SYMMETRIC</code> is like <code class="literal">BETWEEN</code>
    except there is no requirement that the argument to the left of
    <code class="literal">AND</code> be less than or equal to the argument on the right.
    If it is not, those two arguments are automatically swapped, so that
    a nonempty range is always implied.
   </p><p>
    The various variants of <code class="literal">BETWEEN</code> are implemented in
    terms of the ordinary comparison operators, and therefore will work for
    any data type(s) that can be compared.
   </p><div class="note"><h3 class="title">Note</h3><p>
     The use of <code class="literal">AND</code> in the <code class="literal">BETWEEN</code>
     syntax creates an ambiguity with the use of <code class="literal">AND</code> as a
     logical operator.  To resolve this, only a limited set of expression
     types are allowed as the second argument of a <code class="literal">BETWEEN</code>
     clause.  If you need to write a more complex sub-expression
     in <code class="literal">BETWEEN</code>, write parentheses around the
     sub-expression.
    </p></div><p>
    <a id="id-1.5.8.8.14.1" class="indexterm"></a>
    <a id="id-1.5.8.8.14.2" class="indexterm"></a>
    Ordinary comparison operators yield null (signifying <span class="quote"><span class="quote">unknown</span></span>),
    not true or false, when either input is null.  For example,
    <code class="literal">7 = NULL</code> yields null, as does <code class="literal">7 &lt;&gt; NULL</code>.  When
    this behavior is not suitable, use the
    <code class="literal">IS [<span class="optional"> NOT </span>] DISTINCT FROM</code> predicates:
</p><pre class="synopsis">
<em class="replaceable"><code>a</code></em> IS DISTINCT FROM <em class="replaceable"><code>b</code></em>
<em class="replaceable"><code>a</code></em> IS NOT DISTINCT FROM <em class="replaceable"><code>b</code></em>
</pre><p>
    For non-null inputs, <code class="literal">IS DISTINCT FROM</code> is
    the same as the <code class="literal">&lt;&gt;</code> operator.  However, if both
    inputs are null it returns false, and if only one input is
    null it returns true.  Similarly, <code class="literal">IS NOT DISTINCT
    FROM</code> is identical to <code class="literal">=</code> for non-null
    inputs, but it returns true when both inputs are null, and false when only
    one input is null. Thus, these predicates effectively act as though null
    were a normal data value, rather than <span class="quote"><span class="quote">unknown</span></span>.
   </p><p>
    <a id="id-1.5.8.8.15.1" class="indexterm"></a>
    <a id="id-1.5.8.8.15.2" class="indexterm"></a>
    <a id="id-1.5.8.8.15.3" class="indexterm"></a>
    <a id="id-1.5.8.8.15.4" class="indexterm"></a>
    To check whether a value is or is not null, use the predicates:
</p><pre class="synopsis">
<em class="replaceable"><code>expression</code></em> IS NULL
<em class="replaceable"><code>expression</code></em> IS NOT NULL
</pre><p>
    or the equivalent, but nonstandard, predicates:
</p><pre class="synopsis">
<em class="replaceable"><code>expression</code></em> ISNULL
<em class="replaceable"><code>expression</code></em> NOTNULL
</pre><p>
    <a id="id-1.5.8.8.15.7" class="indexterm"></a>
   </p><p>
    Do <span class="emphasis"><em>not</em></span> write
    <code class="literal"><em class="replaceable"><code>expression</code></em> = NULL</code>
    because <code class="literal">NULL</code> is not <span class="quote"><span class="quote">equal to</span></span>
    <code class="literal">NULL</code>.  (The null value represents an unknown value,
    and it is not known whether two unknown values are equal.)
   </p><div class="tip"><h3 class="title">Tip</h3><p>
    Some applications might expect that
    <code class="literal"><em class="replaceable"><code>expression</code></em> = NULL</code>
    returns true if <em class="replaceable"><code>expression</code></em> evaluates to
    the null value.  It is highly recommended that these applications
    be modified to comply with the SQL standard. However, if that
    cannot be done the <a class="xref" href="runtime-config-compatible.html#GUC-TRANSFORM-NULL-EQUALS">transform_null_equals</a>
    configuration variable is available. If it is enabled,
    <span class="productname">PostgreSQL</span> will convert <code class="literal">x =
    NULL</code> clauses to <code class="literal">x IS NULL</code>.
   </p></div><p>
    If the <em class="replaceable"><code>expression</code></em> is row-valued, then
    <code class="literal">IS NULL</code> is true when the row expression itself is null
    or when all the row's fields are null, while
    <code class="literal">IS NOT NULL</code> is true when the row expression itself is non-null
    and all the row's fields are non-null.  Because of this behavior,
    <code class="literal">IS NULL</code> and <code class="literal">IS NOT NULL</code> do not always return
    inverse results for row-valued expressions; in particular, a row-valued
    expression that contains both null and non-null fields will return false
    for both tests.  In some cases, it may be preferable to
    write <em class="replaceable"><code>row</code></em> <code class="literal">IS DISTINCT FROM NULL</code>
    or <em class="replaceable"><code>row</code></em> <code class="literal">IS NOT DISTINCT FROM NULL</code>,
    which will simply check whether the overall row value is null without any
    additional tests on the row fields.
   </p><p>
    <a id="id-1.5.8.8.19.1" class="indexterm"></a>
    <a id="id-1.5.8.8.19.2" class="indexterm"></a>
    <a id="id-1.5.8.8.19.3" class="indexterm"></a>
    <a id="id-1.5.8.8.19.4" class="indexterm"></a>
    <a id="id-1.5.8.8.19.5" class="indexterm"></a>
    <a id="id-1.5.8.8.19.6" class="indexterm"></a>
    Boolean values can also be tested using the predicates
</p><pre class="synopsis">
<em class="replaceable"><code>boolean_expression</code></em> IS TRUE
<em class="replaceable"><code>boolean_expression</code></em> IS NOT TRUE
<em class="replaceable"><code>boolean_expression</code></em> IS FALSE
<em class="replaceable"><code>boolean_expression</code></em> IS NOT FALSE
<em class="replaceable"><code>boolean_expression</code></em> IS UNKNOWN
<em class="replaceable"><code>boolean_expression</code></em> IS NOT UNKNOWN
</pre><p>
    These will always return true or false, never a null value, even when the
    operand is null.
    A null input is treated as the logical value <span class="quote"><span class="quote">unknown</span></span>.
    Notice that <code class="literal">IS UNKNOWN</code> and <code class="literal">IS NOT UNKNOWN</code> are
    effectively the same as <code class="literal">IS NULL</code> and
    <code class="literal">IS NOT NULL</code>, respectively, except that the input
    expression must be of Boolean type.
   </p><p>
    Some comparison-related functions are also available, as shown in <a class="xref" href="functions-comparison.html#FUNCTIONS-COMPARISON-FUNC-TABLE" title="Table 9.3. Comparison Functions">Table 9.3</a>.
   </p><div class="table" id="FUNCTIONS-COMPARISON-FUNC-TABLE"><p class="title"><strong>Table 9.3. Comparison Functions</strong></p><div class="table-contents"><table class="table" summary="Comparison Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
        Function
       </p>
       <p>
        Description
       </p>
       <p>
        Example(s)
       </p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
        <a id="id-1.5.8.8.21.2.2.1.1.1.1" class="indexterm"></a>
        <code class="function">num_nonnulls</code> ( <code class="literal">VARIADIC</code> <code class="type">"any"</code> )
        → <code class="returnvalue">integer</code>
       </p>
       <p>
        Returns the number of non-null arguments.
       </p>
       <p>
        <code class="literal">num_nonnulls(1, NULL, 2)</code><code class="returnvalue">2</code>
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <a id="id-1.5.8.8.21.2.2.2.1.1.1" class="indexterm"></a>
        <code class="function">num_nulls</code> ( <code class="literal">VARIADIC</code> <code class="type">"any"</code> )
        → <code class="returnvalue">integer</code>
       </p>
       <p>
        Returns the number of null arguments.
       </p>
       <p>
        <code class="literal">num_nulls(1, NULL, 2)</code><code class="returnvalue">1</code>
       </p></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions-logical.html" title="9.1. Logical Operators">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="functions-math.html" title="9.3. Mathematical Functions and Operators">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.1. Logical Operators </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 9.3. Mathematical Functions and Operators</td></tr></table></div></body></html>