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Diffstat (limited to 'doc/src/sgml/queries.sgml')
| -rw-r--r-- | doc/src/sgml/queries.sgml | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/doc/src/sgml/queries.sgml b/doc/src/sgml/queries.sgml index bcee9468240..caa9f1b3389 100644 --- a/doc/src/sgml/queries.sgml +++ b/doc/src/sgml/queries.sgml @@ -717,14 +717,24 @@ SELECT * </indexterm> <para> - Subqueries and table functions appearing in <literal>FROM</> can be + Subqueries appearing in <literal>FROM</> can be preceded by the key word <literal>LATERAL</>. This allows them to reference columns provided by preceding <literal>FROM</> items. - (Without <literal>LATERAL</literal>, each <literal>FROM</> item is + (Without <literal>LATERAL</literal>, each subquery is evaluated independently and so cannot cross-reference any other <literal>FROM</> item.) + </para> + + <para> + Table functions appearing in <literal>FROM</> can also be + preceded by the key word <literal>LATERAL</>, but for functions the + key word is optional; the function's arguments can contain references + to columns provided by preceding <literal>FROM</> items in any case. + </para> + + <para> A <literal>LATERAL</literal> item can appear at top level in the - <literal>FROM</> list, or within a <literal>JOIN</> tree; in the latter + <literal>FROM</> list, or within a <literal>JOIN</> tree. In the latter case it can also refer to any items that are on the left-hand side of a <literal>JOIN</> that it is on the right-hand side of. </para> @@ -770,7 +780,9 @@ FROM polygons p1 CROSS JOIN LATERAL vertices(p1.poly) v1, polygons p2 CROSS JOIN LATERAL vertices(p2.poly) v2 WHERE (v1 <-> v2) < 10 AND p1.id != p2.id; </programlisting> - or in several other equivalent formulations. + or in several other equivalent formulations. (As already mentioned, + the <literal>LATERAL</> key word is unnecessary in this example, but + we use it for clarity.) </para> <para> |