Charlotte Pollock <[EMAIL PROTECTED]> writes: > I'm trying to create a aggregate function similar 9but not identical) to > mysql's group_concat.
> What I want to be able to do is pass and order by field to the aggregate so > I can be certain I get the list of strings in the correct order. The way this is usually done in PG is to order the data before it gets to the aggregate function. For the ungrouped case this is easy: SELECT my_concat(foo) FROM (SELECT foo FROM ... ORDER BY something) ss; If you're trying to aggregate within groups it's a bit trickier. The secret is that the ordering of the inner sub-select has to match the outer GROUP BY: SELECT my_concat(foo), bar FROM (SELECT foo,bar FROM ... ORDER BY bar, something) ss GROUP BY bar; In some cases it'll still work with just ORDER BY something, but that depends on which plan type the planner happens to choose, so it's not reliable to leave off the ORDER BY bar. This requires a fairly recent PG ... I think we fixed the planner to make this work properly in 7.4. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq