On Mon, 18 Feb 2013 12:10:00 +0100, Carsten Schäfer <ca_schae...@gmx.de> wrote: >> Actually, I don't know whether Firebird treats coalesce as if OR had >> been used. In some cases, I suspect it in theory could, but >> COALESCE(a, b) IS NULL would have to translate to AND rather than OR. >> Don't know whether this is implemented, or even if it would be >> beneficial if implemented - whenever I use coalesce in a WHERE clause, >> it is very rarely referring to different fields within the same tuple. >> > The comparison with your OR-example gives the same result. > The OR uses both indexes and coalesce is not using the indexes. > That's the problem.
The optimizer in Firebird simply can't do this for a COALESCE. It might work if you have an expression index on COALESCE(apos.f_dat_anlieferung, apos.f_dat_erstellung) (BTW: I am not 100% sure about this). Mark
