Thread: ROW_NUMBER alias
Hi,<br /><br />I needed ROW_NUMBER() in PostGresql and I did find the 'temporary sequence' method as a workaround and i thinkit at least gets the job done relatively well, ... so no problems there. <br /><br />Its just that from a usabilitypoint of view, isn't it better that we provide some kind of an aliasing mechanism here that allows a new user to(unknowingly but) implicitly use a temporary sequence rather than make him use SubQuery with a COUNT(*) and a comparisonoperator (with disastrous performance) instead ?? <br /><br />So for a new user :<br /><br />A query such as this:<br /><br /> SELECT ROW_NUMBER() AS row_number , a, b, c<br /> FROM table<br /> WHERE table_id = 973<br/> ORDER BY record_date;<br /><br />is internally interpreted by the planner as : <br /><br /> CREATE TEMPSEQUENCE rownum; <br /><br /> SELECT nextval('rownum') AS row_number , t.a, t.b, t.c<br /> FROM (<br /> SELECT a, b, c<br /> FROM table<br /> WHERE table_id = 973<br /> ORDER BY record_date<br /> )t;<br /><br /> DROP SEQUENCE rownum;<br /><br /> <br clear="all" />Any ideas ?<br />(Of what I remember, I think tillrecently PostgreSql internally replaced 'MAX(x)' queries with a 'ORDER BY x DESC LIMIT 1' implicitly)<br /><br />--<br/>Robins
I might be told off by some better SQL-User here on the list - still here is my 2 Cents worth.... > I needed ROW_NUMBER() in PostGresql and I did find the 'temporary sequence' > method as a workaround and i think it at least gets the job done relatively you use: > CREATE TEMP SEQUENCE rownum; > SELECT nextval('rownum') AS row_number , t.a, t.b, t.c > FROM ( > SELECT a, b, c > FROM table > WHERE table_id = 973 > ORDER BY record_date > ) t; Doesn't this just return the 973th single record for the current sequence order in your table? I believe:SELECT a, b, c FROM tableoffset 973 limit 1 will accomplish the same result. Stefan -- email: stefan@yukonho.de tel : +49 (0)6232-497631 http://www.yukonho.de
Hi Stefan,
Well that was just an example. That table had a primary key on (id, date). By bad then, coz I guess I should have clarified that earlier.
But what I meant from the example was that it is trivial for the parser to automatically put an enveloping SELECT to add a ROW_NUMBER() field to any user given query.
Regards,
Robins Tharakan
Well that was just an example. That table had a primary key on (id, date). By bad then, coz I guess I should have clarified that earlier.
But what I meant from the example was that it is trivial for the parser to automatically put an enveloping SELECT to add a ROW_NUMBER() field to any user given query.
Regards,
Robins Tharakan
On 5/7/07, Stefan Becker <pgsql@yukonho.de > wrote:
I might be told off by some better SQL-User here on the list -
still here is my 2 Cents worth....
> I needed ROW_NUMBER() in PostGresql and I did find the 'temporary sequence'
> method as a workaround and i think it at least gets the job done relatively
you use:
> CREATE TEMP SEQUENCE rownum;
> SELECT nextval('rownum') AS row_number , t.a, t.b, t.c
> FROM (
> SELECT a, b, c
> FROM table
> WHERE table_id = 973
> ORDER BY record_date
> ) t;
Doesn't this just return the 973th single record for the current
sequence order in your table?
I believe:
SELECT a, b, c FROM table
offset 973 limit 1
will accomplish the same result.
Stefan