Subject Re: [firebird-support] MAX() and index

You need to use a descending index for it (pk can be descending also).

Also change your sql to:
Select first 1 mycol from mytab order by mycol desc
This will have the spected result.

Em 07/09/2015 10:00, "Tim Ward tdw@... [firebird-support]" <> escreveu:

Please can someone explain to me, again, why

select Max(MYCOL) from MYTAB

doesn't use the primary key


Current memory = 3074072
Delta memory = -20
Max memory = 3217516
Elapsed time= 0.27 sec
Buffers = 150
Reads = 1811
Writes 0
Fetches = 894779

of which it is the first field


and instead reads thousands of pages from disk and takes over a quarter
of a second?

(I'm just curious and wanting to understand, really. I'm going to fix
the actual problem with a change of approach, that's needed for other
reasons anyway, which eliminates the problem query.)

Tim Ward