Re: Query with LIMIT clause

From: pgsql-sql-owner(at)postgresql(dot)org [mailto:pgsql-sql-owner(at)postgresql(dot)org]
On Behalf Of JORGE MALDONADO
Sent: Sunday, September 09, 2012 1:26 PM
To: pgsql-sql(at)postgresql(dot)org
Subject: [SQL] Query with LIMIT clause

I have the following records that I get from a query, the fields are date
type in day/month/year format:

-------------------------------------
Initial           Final
Date            Date
-------------------------------------
27/08/2012   04/09/2012
29/08/2012   09/09/2012
28/08/2012   09/09/2012
30/08/2012   09/09/2012
30/08/2012   09/09/2012
27/08/2012   09/09/2012
31/08/2012   09/09/2012
28/08/2012   10/09/2012
05/09/2012   16/09/2012

As you can see, this result is ordered by Final Date. What I need is to get
the last 5 records only. If I use the LIMIT 5 clause I get the first 5. I
have tried an ORDEY BY DESC but the result is the same. I will very much
appreciate your comments.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>.

First, you should really order by both columns, not just "final date". The
ties on 9/9/12 are unordered.

Second, you will indeed need to reverse the sort order and then take the
first 5 records; figuring out and limiting on the last 5 isn't worth the
effort.

SELECT initial_date, final_date
FROM date_source
ORDER BY final_date DESC, initial_date DESC
LIMIT 5

You can put the above into a sub-query and re-order if the final result is
needed in ascending order.

If this doesn't seem to work you will want to provide the exact
query/queries you are trying so that someone may spot what you are doing
wrong.

Dave