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diff --git a/doc/src/sgml/html/functions-comparisons.html b/doc/src/sgml/html/functions-comparisons.html new file mode 100644 index 0000000..68035a5 --- /dev/null +++ b/doc/src/sgml/html/functions-comparisons.html @@ -0,0 +1,213 @@ +<?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>9.24. Row and Array Comparisons</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 V1.79.1" /><link rel="prev" href="functions-subquery.html" title="9.23. Subquery Expressions" /><link rel="next" href="functions-srf.html" title="9.25. Set Returning Functions" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.24. Row and Array Comparisons</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-subquery.html" title="9.23. Subquery Expressions">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 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-srf.html" title="9.25. Set Returning Functions">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="FUNCTIONS-COMPARISONS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.24. Row and Array Comparisons</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="functions-comparisons.html#FUNCTIONS-COMPARISONS-IN-SCALAR">9.24.1. <code class="literal">IN</code></a></span></dt><dt><span class="sect2"><a href="functions-comparisons.html#id-1.5.8.30.15">9.24.2. <code class="literal">NOT IN</code></a></span></dt><dt><span class="sect2"><a href="functions-comparisons.html#id-1.5.8.30.16">9.24.3. <code class="literal">ANY</code>/<code class="literal">SOME</code> (array)</a></span></dt><dt><span class="sect2"><a href="functions-comparisons.html#id-1.5.8.30.17">9.24.4. <code class="literal">ALL</code> (array)</a></span></dt><dt><span class="sect2"><a href="functions-comparisons.html#ROW-WISE-COMPARISON">9.24.5. Row Constructor Comparison</a></span></dt><dt><span class="sect2"><a href="functions-comparisons.html#COMPOSITE-TYPE-COMPARISON">9.24.6. Composite Type Comparison</a></span></dt></dl></div><a id="id-1.5.8.30.2" class="indexterm"></a><a id="id-1.5.8.30.3" class="indexterm"></a><a id="id-1.5.8.30.4" class="indexterm"></a><a id="id-1.5.8.30.5" class="indexterm"></a><a id="id-1.5.8.30.6" class="indexterm"></a><a id="id-1.5.8.30.7" class="indexterm"></a><a id="id-1.5.8.30.8" class="indexterm"></a><a id="id-1.5.8.30.9" class="indexterm"></a><a id="id-1.5.8.30.10" class="indexterm"></a><a id="id-1.5.8.30.11" class="indexterm"></a><a id="id-1.5.8.30.12" class="indexterm"></a><p> + This section describes several specialized constructs for making + multiple comparisons between groups of values. These forms are + syntactically related to the subquery forms of the previous section, + but do not involve subqueries. + The forms involving array subexpressions are + <span class="productname">PostgreSQL</span> extensions; the rest are + <acronym class="acronym">SQL</acronym>-compliant. + All of the expression forms documented in this section return + Boolean (true/false) results. + </p><div class="sect2" id="FUNCTIONS-COMPARISONS-IN-SCALAR"><div class="titlepage"><div><div><h3 class="title">9.24.1. <code class="literal">IN</code></h3></div></div></div><pre class="synopsis"> +<em class="replaceable"><code>expression</code></em> IN (<em class="replaceable"><code>value</code></em> [<span class="optional">, ...</span>]) +</pre><p> + The right-hand side is a parenthesized list + of scalar expressions. The result is <span class="quote">“<span class="quote">true</span>”</span> if the left-hand expression's + result is equal to any of the right-hand expressions. This is a shorthand + notation for + +</p><pre class="synopsis"> +<em class="replaceable"><code>expression</code></em> = <em class="replaceable"><code>value1</code></em> +OR +<em class="replaceable"><code>expression</code></em> = <em class="replaceable"><code>value2</code></em> +OR +... +</pre><p> + </p><p> + Note that if the left-hand expression yields null, or if there are + no equal right-hand values and at least one right-hand expression yields + null, the result of the <code class="token">IN</code> construct will be null, not false. + This is in accordance with SQL's normal rules for Boolean combinations + of null values. + </p></div><div class="sect2" id="id-1.5.8.30.15"><div class="titlepage"><div><div><h3 class="title">9.24.2. <code class="literal">NOT IN</code></h3></div></div></div><pre class="synopsis"> +<em class="replaceable"><code>expression</code></em> NOT IN (<em class="replaceable"><code>value</code></em> [<span class="optional">, ...</span>]) +</pre><p> + The right-hand side is a parenthesized list + of scalar expressions. The result is <span class="quote">“<span class="quote">true</span>”</span> if the left-hand expression's + result is unequal to all of the right-hand expressions. This is a shorthand + notation for + +</p><pre class="synopsis"> +<em class="replaceable"><code>expression</code></em> <> <em class="replaceable"><code>value1</code></em> +AND +<em class="replaceable"><code>expression</code></em> <> <em class="replaceable"><code>value2</code></em> +AND +... +</pre><p> + </p><p> + Note that if the left-hand expression yields null, or if there are + no equal right-hand values and at least one right-hand expression yields + null, the result of the <code class="token">NOT IN</code> construct will be null, not true + as one might naively expect. + This is in accordance with SQL's normal rules for Boolean combinations + of null values. + </p><div class="tip"><h3 class="title">Tip</h3><p> + <code class="literal">x NOT IN y</code> is equivalent to <code class="literal">NOT (x IN y)</code> in all + cases. However, null values are much more likely to trip up the novice when + working with <code class="token">NOT IN</code> than when working with <code class="token">IN</code>. + It is best to express your condition positively if possible. + </p></div></div><div class="sect2" id="id-1.5.8.30.16"><div class="titlepage"><div><div><h3 class="title">9.24.3. <code class="literal">ANY</code>/<code class="literal">SOME</code> (array)</h3></div></div></div><pre class="synopsis"> +<em class="replaceable"><code>expression</code></em> <em class="replaceable"><code>operator</code></em> ANY (<em class="replaceable"><code>array expression</code></em>) +<em class="replaceable"><code>expression</code></em> <em class="replaceable"><code>operator</code></em> SOME (<em class="replaceable"><code>array expression</code></em>) +</pre><p> + The right-hand side is a parenthesized expression, which must yield an + array value. + The left-hand expression + is evaluated and compared to each element of the array using the + given <em class="replaceable"><code>operator</code></em>, which must yield a Boolean + result. + The result of <code class="token">ANY</code> is <span class="quote">“<span class="quote">true</span>”</span> if any true result is obtained. + The result is <span class="quote">“<span class="quote">false</span>”</span> if no true result is found (including the + case where the array has zero elements). + </p><p> + If the array expression yields a null array, the result of + <code class="token">ANY</code> will be null. If the left-hand expression yields null, + the result of <code class="token">ANY</code> is ordinarily null (though a non-strict + comparison operator could possibly yield a different result). + Also, if the right-hand array contains any null elements and no true + comparison result is obtained, the result of <code class="token">ANY</code> + will be null, not false (again, assuming a strict comparison operator). + This is in accordance with SQL's normal rules for Boolean combinations + of null values. + </p><p> + <code class="token">SOME</code> is a synonym for <code class="token">ANY</code>. + </p></div><div class="sect2" id="id-1.5.8.30.17"><div class="titlepage"><div><div><h3 class="title">9.24.4. <code class="literal">ALL</code> (array)</h3></div></div></div><pre class="synopsis"> +<em class="replaceable"><code>expression</code></em> <em class="replaceable"><code>operator</code></em> ALL (<em class="replaceable"><code>array expression</code></em>) +</pre><p> + The right-hand side is a parenthesized expression, which must yield an + array value. + The left-hand expression + is evaluated and compared to each element of the array using the + given <em class="replaceable"><code>operator</code></em>, which must yield a Boolean + result. + The result of <code class="token">ALL</code> is <span class="quote">“<span class="quote">true</span>”</span> if all comparisons yield true + (including the case where the array has zero elements). + The result is <span class="quote">“<span class="quote">false</span>”</span> if any false result is found. + </p><p> + If the array expression yields a null array, the result of + <code class="token">ALL</code> will be null. If the left-hand expression yields null, + the result of <code class="token">ALL</code> is ordinarily null (though a non-strict + comparison operator could possibly yield a different result). + Also, if the right-hand array contains any null elements and no false + comparison result is obtained, the result of <code class="token">ALL</code> + will be null, not true (again, assuming a strict comparison operator). + This is in accordance with SQL's normal rules for Boolean combinations + of null values. + </p></div><div class="sect2" id="ROW-WISE-COMPARISON"><div class="titlepage"><div><div><h3 class="title">9.24.5. Row Constructor Comparison</h3></div></div></div><pre class="synopsis"> +<em class="replaceable"><code>row_constructor</code></em> <em class="replaceable"><code>operator</code></em> <em class="replaceable"><code>row_constructor</code></em> +</pre><p> + Each side is a row constructor, + as described in <a class="xref" href="sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS" title="4.2.13. Row Constructors">Section 4.2.13</a>. + The two row values must have the same number of fields. + Each side is evaluated and they are compared row-wise. Row constructor + comparisons are allowed when the <em class="replaceable"><code>operator</code></em> is + <code class="literal">=</code>, + <code class="literal"><></code>, + <code class="literal"><</code>, + <code class="literal"><=</code>, + <code class="literal">></code> or + <code class="literal">>=</code>. + Every row element must be of a type which has a default B-tree operator + class or the attempted comparison may generate an error. + </p><div class="note"><h3 class="title">Note</h3><p> + Errors related to the number or types of elements might not occur if + the comparison is resolved using earlier columns. + </p></div><p> + The <code class="literal">=</code> and <code class="literal"><></code> cases work slightly differently + from the others. Two rows are considered + equal if all their corresponding members are non-null and equal; the rows + are unequal if any corresponding members are non-null and unequal; + otherwise the result of the row comparison is unknown (null). + </p><p> + For the <code class="literal"><</code>, <code class="literal"><=</code>, <code class="literal">></code> and + <code class="literal">>=</code> cases, the row elements are compared left-to-right, + stopping as soon as an unequal or null pair of elements is found. + If either of this pair of elements is null, the result of the + row comparison is unknown (null); otherwise comparison of this pair + of elements determines the result. For example, + <code class="literal">ROW(1,2,NULL) < ROW(1,3,0)</code> + yields true, not null, because the third pair of elements are not + considered. + </p><div class="note"><h3 class="title">Note</h3><p> + Prior to <span class="productname">PostgreSQL</span> 8.2, the + <code class="literal"><</code>, <code class="literal"><=</code>, <code class="literal">></code> and <code class="literal">>=</code> + cases were not handled per SQL specification. A comparison like + <code class="literal">ROW(a,b) < ROW(c,d)</code> + was implemented as + <code class="literal">a < c AND b < d</code> + whereas the correct behavior is equivalent to + <code class="literal">a < c OR (a = c AND b < d)</code>. + </p></div><pre class="synopsis"> +<em class="replaceable"><code>row_constructor</code></em> IS DISTINCT FROM <em class="replaceable"><code>row_constructor</code></em> +</pre><p> + This construct is similar to a <code class="literal"><></code> row comparison, + but it does not yield null for null inputs. Instead, any null value is + considered unequal to (distinct from) any non-null value, and any two + nulls are considered equal (not distinct). Thus the result will + either be true or false, never null. + </p><pre class="synopsis"> +<em class="replaceable"><code>row_constructor</code></em> IS NOT DISTINCT FROM <em class="replaceable"><code>row_constructor</code></em> +</pre><p> + This construct is similar to a <code class="literal">=</code> row comparison, + but it does not yield null for null inputs. Instead, any null value is + considered unequal to (distinct from) any non-null value, and any two + nulls are considered equal (not distinct). Thus the result will always + be either true or false, never null. + </p></div><div class="sect2" id="COMPOSITE-TYPE-COMPARISON"><div class="titlepage"><div><div><h3 class="title">9.24.6. Composite Type Comparison</h3></div></div></div><pre class="synopsis"> +<em class="replaceable"><code>record</code></em> <em class="replaceable"><code>operator</code></em> <em class="replaceable"><code>record</code></em> +</pre><p> + The SQL specification requires row-wise comparison to return NULL if the + result depends on comparing two NULL values or a NULL and a non-NULL. + <span class="productname">PostgreSQL</span> does this only when comparing the + results of two row constructors (as in + <a class="xref" href="functions-comparisons.html#ROW-WISE-COMPARISON" title="9.24.5. Row Constructor Comparison">Section 9.24.5</a>) or comparing a row constructor + to the output of a subquery (as in <a class="xref" href="functions-subquery.html" title="9.23. Subquery Expressions">Section 9.23</a>). + In other contexts where two composite-type values are compared, two + NULL field values are considered equal, and a NULL is considered larger + than a non-NULL. This is necessary in order to have consistent sorting + and indexing behavior for composite types. + </p><p> + Each side is evaluated and they are compared row-wise. Composite type + comparisons are allowed when the <em class="replaceable"><code>operator</code></em> is + <code class="literal">=</code>, + <code class="literal"><></code>, + <code class="literal"><</code>, + <code class="literal"><=</code>, + <code class="literal">></code> or + <code class="literal">>=</code>, + or has semantics similar to one of these. (To be specific, an operator + can be a row comparison operator if it is a member of a B-tree operator + class, or is the negator of the <code class="literal">=</code> member of a B-tree operator + class.) The default behavior of the above operators is the same as for + <code class="literal">IS [ NOT ] DISTINCT FROM</code> for row constructors (see + <a class="xref" href="functions-comparisons.html#ROW-WISE-COMPARISON" title="9.24.5. Row Constructor Comparison">Section 9.24.5</a>). + </p><p> + To support matching of rows which include elements without a default + B-tree operator class, the following operators are defined for composite + type comparison: + <code class="literal">*=</code>, + <code class="literal">*<></code>, + <code class="literal">*<</code>, + <code class="literal">*<=</code>, + <code class="literal">*></code>, and + <code class="literal">*>=</code>. + These operators compare the internal binary representation of the two + rows. Two rows might have a different binary representation even + though comparisons of the two rows with the equality operator is true. + The ordering of rows under these comparison operators is deterministic + but not otherwise meaningful. These operators are used internally + for materialized views and might be useful for other specialized + purposes such as replication and B-Tree deduplication (see <a class="xref" href="btree-implementation.html#BTREE-DEDUPLICATION" title="63.4.2. Deduplication">Section 63.4.2</a>). They are not intended to be + generally useful for writing queries, though. + </p></div></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions-subquery.html" title="9.23. Subquery Expressions">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-srf.html" title="9.25. Set Returning Functions">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.23. 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