--- In firebird-support@yahoogroups.com, Svein Erling Tysvær
<svein.erling.tysvaer@k...> wrote:

> select ...
> from wb_prg_run w inner join objectmap m on (w.objid = m.objid)
> inner join ch_pos_charge p on (m.to_objid = p.objid+'')
>
> prevents using an index for p.objid in the JOIN ... ON clause (if
> p.objid isn't a string, you may have to use 0 rather than ''). Of
> course, a WHERE clause may make this index useful again, but the

above

> change is a strong hint to use P as the first table in the plan.

I tried this, but +'' is not accepted by sql parser. But after some
research in the back-ends of my memory I remembered that to concat
strings one has to use ||. p.objid||'' is working so far, the
optimizer is walking as i want it now.

-- Joja