Re: Preserving order through an inner join

Kevin Jardine <kevinjardine(at)yahoo(dot)com> writes:
> I have a query structured like this:
> SELECT stuff FROM
> (SELECT more stuff FROM
> table1
> ORDER BY field1) AS q1
> INNER JOIN table2 ON ( ... )

> and have found that the INNER JOIN is ignoring the order set for q1.

> The final results are not ordered by field1.

Indeed. Many of the possible join techniques won't preserve that ordering.

> This works for other databases (eg. MySQL and Sqllite3) but not PostgreSQL.

It might sometimes accidentally fail to fail, but I think you'll find
that there are *no* SQL databases where this is guaranteed to work the
way you expect. The SQL standard explicitly disavows any particular
output row order unless there is a top-level ORDER BY. (In fact,
unless things have changed recently an ORDER BY in a sub-select isn't
even legal per spec.)

> I can make some small changes to the query structure as long as it works for the other DBs as well. Moving the ORDER BY outside q1 would be a large amount of work, however (these queries are generated by a program), so I am hoping that there is a simpler solution.

Nope, that's what you need to do.

regards, tom lane