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Diffstat (limited to 'doc/src/sgml/queries.sgml')
| -rw-r--r-- | doc/src/sgml/queries.sgml | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/doc/src/sgml/queries.sgml b/doc/src/sgml/queries.sgml index a326960ff4d..2736868fb06 100644 --- a/doc/src/sgml/queries.sgml +++ b/doc/src/sgml/queries.sgml @@ -1145,10 +1145,36 @@ SELECT product_id, p.name, (sum(s.units) * p.price) AS sales <para> In strict SQL, <literal>GROUP BY</literal> can only group by columns of - the source table but <productname>PostgreSQL</productname> extends + the source table, but <productname>PostgreSQL</productname> extends this to also allow <literal>GROUP BY</literal> to group by columns in the select list. Grouping by value expressions instead of simple - column names is also allowed. + column names is also allowed (but <literal>GROUP BY</literal> + expressions cannot contain aggregate functions or window functions). + </para> + + <para> + PostgreSQL also supports the syntax <literal>GROUP BY ALL</literal>, + which is equivalent to explicitly writing all select-list entries that + do not contain either an aggregate function or a window function. + This can greatly simplify ad-hoc exploration of data. + As an example, these queries are equivalent: +<screen> +<prompt>=></prompt> <userinput>SELECT a, b, a + b, sum(c) FROM test1 GROUP BY ALL;</userinput> + a | b | ?column? | sum +---+---+----------+---- + 1 | 4 | 5 | 9 + 2 | 5 | 7 | 12 + 3 | 6 | 9 | 15 +(3 rows) + +<prompt>=></prompt> <userinput>SELECT a, b, a + b, sum(c) FROM test1 GROUP BY a, b, a + b;</userinput> + a | b | ?column? | sum +---+---+----------+---- + 1 | 4 | 5 | 9 + 2 | 5 | 7 | 12 + 3 | 6 | 9 | 15 +(3 rows) +</screen> </para> <indexterm> |