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doc: move ROW IS NULL examples to a different chapter
Also add examples. Reported-by: Wolfgang Walther Discussion: https://postgr.es/m/21ff8e9c-627a-f949-fb00-a41b9ddcc9d3@technowledgy.de Backpatch-through: master
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@@ -2479,17 +2479,12 @@ SELECT getf1(CAST(ROW(11,'this is a test',2.5) AS myrowtype));
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<para>
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Row constructors can be used to build composite values to be stored
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in a composite-type table column, or to be passed to a function that
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accepts a composite parameter. Also,
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it is possible to compare two row values or test a row with
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<literal>IS NULL</literal> or <literal>IS NOT NULL</literal>, for example:
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<programlisting>
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SELECT ROW(1,2.5,'this is a test') = ROW(1, 3, 'not the same');
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SELECT ROW(table.*) IS NULL FROM table; -- detect all-null rows
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</programlisting>
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For more detail see <xref linkend="functions-comparisons"/>.
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Row constructors can also be used in connection with subqueries,
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as discussed in <xref linkend="functions-subquery"/>.
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accepts a composite parameter. Also, it is possible to test rows
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using the standard comparison operators as described in <xref
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linkend="functions-comparison"/>, to compare one row against another
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as described in <xref linkend="functions-comparisons"/>, and to
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use them in connection with subqueries, as discussed in <xref
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linkend="functions-subquery"/>,
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</para>
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</sect2>
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