From: | "paul butler" <paul(at)entropia(dot)co(dot)uk> |
---|---|
To: | Jean-Christian Imbeault <jc(at)mega-bucks(dot)co(dot)jp> |
Cc: | pgsql-novice(at)postgresql(dot)org |
Subject: | Re: select distinct() question |
Date: | 2003-04-18 05:28:21 |
Message-ID: | 3E9F9B05.20619.240391D6@localhost |
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Lists: | pgsql-novice |
Date sent: Fri, 18 Apr 2003 12:49:26 +0900
From: Jean-Christian Imbeault <jc(at)mega-bucks(dot)co(dot)jp>
To: pgsql-novice(at)postgresql(dot)org
Subject: [NOVICE] select distinct() question
As I understand it, distinct applies to all distinct combinations of columns specified.
SQL92 allows for multiple distinct on aggregates only (and this can be quite a tricky
area).
so for a table:
id | x
-----+-------
124 | type1
124 | type1
124 | type2
124 | type2
124 | type2
124 | type2
58 | type3
58 | type3
58 | type3
58 | type2
select distinct (id),x from cv;
id | x
-----+------
58 | type2
58 | type3
124 | type1
124 | type2
124 | type3
select distinct (id) from cv;
id
-----
58
124
select distinct x from cv;
x
------
type2
type3
type1
so your result suggests there is at least one of each tuple with values:
prod_id | date_received
---------+---------------
10994 | 2003-04-02
prod_id | date_received
---------+---------------
10994 | 2003-04-02
prod_id | date_received
---------+---------------
12445 | 2003-04-08
prod_id | date_received
---------+---------------
12445 |
hope this helps
Paul Butler
> I observed the following for one of my queries:
>
> TEST=# select distinct(prod_id), date_received from invoice_li;
> prod_id | date_received
> ---------+---------------
> 10994 | 2003-04-02
> 12445 | 2003-04-08
> 12445 |
> (3 rows)
>
>
> Is this the correct behaviour for a select distinct()?
>
> I tried understanding what the SQL standard says but was thoroughly
> confused ;)
>
> Jean-Christian Imbeault
>
>
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