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Commit3d28498

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Document IS DISTINCT FROM in a more obvious place, and add some more
index entries for IS-foo constructs.
1 parent3b6cc1a commit3d28498

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2 files changed

+86
-9
lines changed

2 files changed

+86
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‎doc/src/sgml/func.sgml‎

Lines changed: 75 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
2-
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.220 2004/10/04 08:15:41 neilc Exp $
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$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.221 2004/10/26 22:16:11 tgl Exp $
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PostgreSQL documentation
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-->
55

@@ -283,6 +283,18 @@ PostgreSQL documentation
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</para>
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<para>
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<indexterm>
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<primary>IS NULL</primary>
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</indexterm>
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<indexterm>
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<primary>IS NOT NULL</primary>
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</indexterm>
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<indexterm>
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<primary>ISNULL</primary>
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</indexterm>
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<indexterm>
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<primary>NOTNULL</primary>
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</indexterm>
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To check whether a value is or is not null, use the constructs
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<synopsis>
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<replaceable>expression</replaceable> IS NULL
@@ -305,6 +317,7 @@ PostgreSQL documentation
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behavior conforms to the SQL standard.
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</para>
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<tip>
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<para>
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Some applications may expect that
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<literal><replaceable>expression</replaceable> = NULL</literal>
@@ -318,8 +331,43 @@ PostgreSQL documentation
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the default behavior in <productname>PostgreSQL</productname>
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releases 6.5 through 7.1.
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</para>
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</tip>
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<para>
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<indexterm>
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<primary>IS DISTINCT FROM</primary>
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</indexterm>
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The ordinary comparison operators yield null (signifying <quote>unknown</>)
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when either input is null. Another way to do comparisons is with the
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<literal>IS DISTINCT FROM</literal> construct:
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<synopsis>
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<replaceable>expression</replaceable> IS DISTINCT FROM <replaceable>expression</replaceable>
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</synopsis>
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For non-null inputs this is the same as the <literal>&lt;&gt;</> operator.
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However, when both inputs are null it will return false, and when just
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one input is null it will return true. Thus it effectively acts as though
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null were a normal data value, rather than <quote>unknown</>.
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</para>
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<para>
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<indexterm>
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<primary>IS TRUE</primary>
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</indexterm>
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<indexterm>
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<primary>IS NOT TRUE</primary>
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</indexterm>
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<indexterm>
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<primary>IS FALSE</primary>
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</indexterm>
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<indexterm>
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<primary>IS NOT FALSE</primary>
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</indexterm>
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<indexterm>
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<primary>IS UNKNOWN</primary>
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</indexterm>
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<indexterm>
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<primary>IS NOT UNKNOWN</primary>
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</indexterm>
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Boolean values can also be tested using the constructs
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<synopsis>
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<replaceable>expression</replaceable> IS TRUE
@@ -329,9 +377,13 @@ PostgreSQL documentation
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<replaceable>expression</replaceable> IS UNKNOWN
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<replaceable>expression</replaceable> IS NOT UNKNOWN
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</synopsis>
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Theseare similar to <literal>IS NULL</literal> in that they will
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always return true or false, never a null value, even when theoperand is null.
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Thesewill always return true or false, never a null value, even when the
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operand is null.
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A null input is treated as the logical value <quote>unknown</>.
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Notice that <literal>IS UNKNOWN</> and <literal>IS NOT UNKNOWN</> are
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effectively the same as <literal>IS NULL</literal> and
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<literal>IS NOT NULL</literal>, respectively, except that the input
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expression must be of Boolean type.
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</para>
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</sect1>
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@@ -7344,7 +7396,7 @@ SELECT col1 FROM tab1
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</sect2>
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<sect2>
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<title><literal>NOT IN</literal></title>
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<title><literal>NOT IN</literal></title>
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<synopsis>
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<replaceable>expression</replaceable> NOT IN (<replaceable>subquery</replaceable>)
@@ -7538,9 +7590,9 @@ SELECT col1 FROM tab1
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<sect2>
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<title>Row-wise Comparison</title>
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<indexterm>
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<indexterm zone="functions-subquery">
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<primary>comparison</primary>
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<secondary>of rows</secondary>
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<secondary>subquery result row</secondary>
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</indexterm>
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<synopsis>
@@ -7594,6 +7646,23 @@ SELECT col1 FROM tab1
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<primary>SOME</primary>
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</indexterm>
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<indexterm>
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<primary>comparison</primary>
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<secondary>row-wise</secondary>
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</indexterm>
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<indexterm>
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<primary>IS DISTINCT FROM</primary>
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</indexterm>
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<indexterm>
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<primary>IS NULL</primary>
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</indexterm>
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<indexterm>
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<primary>IS NOT NULL</primary>
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</indexterm>
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<para>
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This section describes several specialized constructs for making
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multiple comparisons between groups of values. These forms are

‎doc/src/sgml/syntax.sgml‎

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@@ -1,5 +1,5 @@
11
<!--
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$PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.95 2004/09/20 22:48:25 tgl Exp $
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$PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.96 2004/10/26 22:16:12 tgl Exp $
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-->
44

55
<chapter id="sql-syntax">
@@ -1421,6 +1421,10 @@ SELECT name, (SELECT max(pop) FROM cities WHERE cities.state = states.name)
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<secondary>constructor</secondary>
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</indexterm>
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<indexterm>
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<primary>ARRAY</primary>
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</indexterm>
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<para>
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An array constructor is an expression that builds an
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array value from values for its member elements. A simple array
@@ -1521,13 +1525,17 @@ SELECT ARRAY(SELECT oid FROM pg_proc WHERE proname LIKE 'bytea%');
15211525
<secondary>constructor</secondary>
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</indexterm>
15231527

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<indexterm>
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<primary>ROW</primary>
1530+
</indexterm>
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<para>
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A row constructor is an expression that builds a row value (also
15261534
called a composite value) from values
15271535
for its member fields. A row constructor consists of the key word
1528-
<literal>ROW</literal>, a left parenthesis <literal>(</>, zero or more
1536+
<literal>ROW</literal>, a left parenthesis, zero or more
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expressions (separated by commas) for the row field values, and finally
1530-
a right parenthesis <literal>)</>. For example,
1538+
a right parenthesis. For example,
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<programlisting>
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SELECT ROW(1,2.5,'this is a test');
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</programlisting>

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