Hi Set,

First i didn't read all messages back in this thread, but you've my attention ;-)

> I don't understand how the optimizer works in cases like yours (SELECT
> FIRST ... ORDER BY ... with a where clause that isn't selective at all).

I don't have enough information too tell what happen on this query, because i don't see a PLAN or a
full query. However i'll give it a try:

SELECT
FIRST 20
SomeFields
FROM
TableX
WHERE
NotIndexField = :param
ORDER BY
FieldA, FieldID

Above query could only use an index for _ordering_ when "FieldA, FieldID" are in 1 index and also in
exactly the same order as direction (ASC/DESC). The PLAN should tell you this immediately. When
you're only fetching a few records with the FIRST/SKIP clause then an index is very helpfull for
retrieval.
Hope this helps somewhat else give some more information about what you want to achieve.

Arno Brinkman
ABVisie

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