Re: Ordinal value of row within set returned by a query?

Thank you, and please keep up the excellent awesome brilliant work on 
the amazing product which is pgsql.

On Thursday, April 17, 2003, at 03:35 PM, Tom Lane wrote:

> Randall Lucas <rlucas@tercent.net> writes:
>> I'm puzzling over whether it is possible within SQL alone to determine
>> the ordinal position of a row within the set returned by a query.  It
>> seems clear to me that pgsql "knows" what position in a set a
>> particular tuple holds, since one can OFFSET, ORDER BY, and LIMIT;
>> however, I can't seem to find a function or "hidden field" that will
>> return this.
>
> That's because there isn't one.
>
> The traditional hack for this has been along the lines of
>
>     create temp sequence foo;
>
>     select nextval('foo'), * from
>     (select ... whatever ... order by something) ss;
>
>     drop sequence foo;
>
> which is illegal per the SQL spec (you can't ORDER BY in a subselect
> according to spec), but it's the only way that you can do computation
> after a sort pass.  In a single-level SELECT, ORDER BY happens after
> the computation of the SELECT output values.
>
> Usually it's a lot easier to plaster on the row numbers on the client
> side, though.
>
>> What I would like is something along these lines:  I wish to ORDER BY
>> an ordinal field that is likely to be present, but may not be present,
>> and then by a unique value to ensure stability of ordering.
>
> Why don't you order by the ordinal field, then the table's primary key?
> (If it hasn't got a primary key, maybe it should.)
>
>             regards, tom lane
>