Re: Group by bug? - Mailing list pgsql-general

From wd
Subject Re: Group by bug?
Date
Msg-id CABexzmgz5ZGJXPSo7i8yuwaayNSE5w55zLUAODZp6jLbGVAR9w@mail.gmail.com
Whole thread Raw
In response to Re: Group by bug?  (Jov <zhao6014@gmail.com>)
List pgsql-general
Oh, I see, thanks for your quick reply.


On Fri, Dec 28, 2012 at 3:47 PM, Jov <zhao6014@gmail.com> wrote:


2012/12/28 wd <wd@wdicc.com>
hi,

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)

---- this sql will not group by the case result.
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. 

pgsql-general by date:

Previous
From: Jov
Date:
Subject: Re: Group by bug?
Next
From: Amit Kapila
Date:
Subject: Re: Cursor fetch Problem.