2012/12/28 wd <wd@xxxxxxxxx>
hi,---- this sql will not group by the case result.
wd_test=# \d t1
Table "public.t1"
Column | Type | Modifiers
--------+---------+-------------------------------------------------
id | integer | not null default nextval('t1_id_seq'::regclass)
tag | text |
wd_test=# select * from t1;
id | tag
----+-----
1 | a
2 | a
3 | b
4 | c
5 | b
(5 rows)wd_test=# select case t1.tag when 'a' then '1' else '0' end as tag, count(*) from t1 group by tag;
here the group by key tag is t1.tag,not the tag int the select list
tag | count
-----+-------
0 | 1
0 | 2
1 | 2
(3 rows)
---- this sql will group by the case result.
wd_test=# select case t1.tag when 'a' then '1' else '0' end as ttag, count(*) from t1 group by ttag;
here the ttag is the select list ttag,it is equal with group by 1.
ttag | count
------+-------
0 | 3
1 | 2
(2 rows)
GROUP BY will condense into a single row all selected rows that share the same values for the grouped expressions. _expression_ can be an input column name, or the name or ordinal number of an output column (SELECT list item), or an arbitrary _expression_ formed from input-column values. In case of ambiguity, a GROUP BY name will be interpreted as an input-column name rather than an output column name.
so it is not a bug.
