On Oct 17, 2006, at 15:19, Peter Eisentraut wrote:

Mark Woodward wrote:
Shouldn't this work?

select ycis_id, min(tindex), avg(tindex) from y where ycis_id = 15;

ERROR:  column "y.ycis_id" must appear in the GROUP BY clause or be
used in an aggregate function

This would require a great deal of special-casing, in particular
knowledge of the = operator, and then the restriction to a particular
form of the WHERE clause.  For overall consistency, I don't think this
should be allowed.

In this particular case, the client constructing the query *knows* the value of ycis_id (since the client is generating the "ycis_id = 15" clause). It's technically just a waste of bandwidth and server resources to recalculate it. If you really want to replicate the output of the query you proposed, you could rewrite it on the client as:

select 15 as ycis_id, min(tindex), avg(tindex) from y where ycis_id = 15;

You could argue that the server should do this for you, but it seems ugly to do in the general case. And, like Peter points out, would need a lot of special-casing. I guess the parser could do it for expressions in the SELECT clause that exactly match expressions in the WHERE clause.


- Chris

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