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Home > Forums > Programmers > DBMS Packages > PostgreSQL Inc.: PostgreSQL Forum

SELECT DISTINCT and ORDER BY

thread699-1261181
Read More Threads Like This One
abenstex (Programmer)
1 Aug 06 4:46
Hi everyone,

i have amongst others the columns pid(varchar) and insertDate(timestamp) and would like to obtain all distinct pid values ordered by insertDate. The problem, though, is that with the following query

CODE

select distinct pid, insertDate from mytable order by insertDate
returns all distinct combinations for pid and insertDate. But i want ONLY the distinct pids ordered by the timestamp.

Any advice is really appreciated.
ceco (IS/IT--Management)
1 Aug 06 5:03
try SELECT DISTINCT ON (pid) pid, insertDate ....

see for details
http://www.postgresql.org/docs/8.1/interactive/sql-select.html
abenstex (Programmer)
1 Aug 06 5:20
I tried that but it seems not to work with order by. That's the error i get when i include the order by:
SELECT DISTINCT ON expressions must match initial ORDER BY expressions
feherke (Programmer)
1 Aug 06 6:05
Hi

As far as I remember, this was my first question on Tek-Tips in thread699-434666. smile

But since then, I did not find out the solution. The best workaround is using sub-select :

CODE

select * from (
  select distinct on (pid) pid, insertDate from mytable
) foo order by insertDate

Feherke.
http://rootshell.be/~feherke/
abenstex (Programmer)
1 Aug 06 6:18
Thanks that worked!!
Read More Threads Like This One

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