diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/queries.sgml | 20 | ||||
| -rw-r--r-- | doc/src/sgml/ref/select.sgml | 41 |
2 files changed, 44 insertions, 17 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> diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml index 26d511fad8c..0f9d52753d8 100644 --- a/doc/src/sgml/ref/select.sgml +++ b/doc/src/sgml/ref/select.sgml @@ -504,18 +504,28 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ] <varlistentry> <term><literal>LATERAL</literal></term> <listitem> - <para>The <literal>LATERAL</literal> key word can precede a - sub-<command>SELECT</command> or function-call <literal>FROM</> - item. This allows the sub-<command>SELECT</command> or function - expression to refer to columns of <literal>FROM</> items that appear - before it in the <literal>FROM</> list. (Without - <literal>LATERAL</literal>, each <literal>FROM</> item is evaluated - independently and so cannot cross-reference any other - <literal>FROM</> item.) A <literal>LATERAL</literal> item can - appear at top level in the <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> + The <literal>LATERAL</literal> key word can precede a + sub-<command>SELECT</command> <literal>FROM</> item. This allows the + sub-<command>SELECT</command> to refer to columns of <literal>FROM</> + items that appear before it in the <literal>FROM</> list. (Without + <literal>LATERAL</literal>, each sub-<command>SELECT</command> is + evaluated independently and so cannot cross-reference any other + <literal>FROM</> item.) + </para> + + <para> + <literal>LATERAL</literal> can also precede a function-call + <literal>FROM</> item, but in this case it is a noise word, because + the function expression can refer to earlier <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 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> <para> @@ -1738,7 +1748,12 @@ SELECT distributors.* WHERE distributors.name = 'Westward'; sub-<command>SELECT</command>; that is, the syntax <literal>FROM <replaceable>func</>(...) <replaceable>alias</></literal> is approximately equivalent to - <literal>FROM (SELECT <replaceable>func</>(...)) <replaceable>alias</></literal>. + <literal>FROM LATERAL (SELECT <replaceable>func</>(...)) <replaceable>alias</></literal>. + Note that <literal>LATERAL</> is considered to be implicit; this is + because the standard requires <literal>LATERAL</> semantics for an + <literal>UNNEST()</> item in <literal>FROM</>. + <productname>PostgreSQL</productname> treats <literal>UNNEST()</> the + same as other set-returning functions. </para> </refsect2> |