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 t...@telensa.com [firebird-support]" < firebird-support@yahoogroups.com> escreveu:
> > > Please can someone explain to me, again, why > > select Max(MYCOL) from MYTAB > > doesn't use the primary key > > PLAN (MYTAB NATURAL) > > 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 > > CONSTRAINT PK_MYTABPRIMARY KEY (MYCOL, OTHERCOL) > > 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 > > >
