Re: SQL to only check for existence:

["rick baird" <rick.baird@xxxxxxxxx>]

Vern,

On 4/18/06, vhamberg@xxxxxxxxxxx <vhamberg@xxxxxxxxxxx> wrote:
> Are you sure there's no where clause? It's in the subquery (where exists...), 
> I think.
>
> The point is that "where exists" does not do a full table scan to return a 
> result, therefore it is very fast.

I meant, no where clause in the subselect inside the where exists().

mine had a LIKE '____xxxx___' compare in the subselect, which runs
much slower, especially if the first match is deep into the access
path it chooses.   I tested it - if the first match was towards the
beginning of the chosen access path, it found it sub-second.  near the
end, it was more like 6-10 secs.

> I'm not sure whether the select into is faster - probably no noticeable 
> difference.

no, I don't think select '1' is any faster, I just like it better.  it
returns 1 to my indicator variable when successful, and I can test for
(not $found).

I tried both ways and found no noticable difference.

> To explain further, the "select 1 from..." is working against a single-row 
> table, hence it
> returns a single value and can be assigned to the host variable (I think that 
> makes
> sense). It'd probably fail if the "select 1 from..." returned multiple rows.

my first attempt (without the sysdummy1 file) did fail.  I'd never
heard of the sysdummy1 file.

> The idea is to test for records in a file, so that file name goes into the 
> innermost select.
>
> HTH

it does, thanks!

Rick