Re: DBA FIGHT

Originally posted by Denaro
> I am sorry but the hot make me crazy.
>
> the right samples are:
>
> select *
> from table1 t1
> where t1.a in
> (
> select t2.a
> from fable2 t2
> where t1.b = t1.b
> );
>
> select *
> from table1 t1, table2 t2
> where t1.a in t2.a
> and t1.b = t1.b
>

Those are still not right: fable2? t1.b = t1.b?

Let's assume you meant:

select t1.*
from table1 t1
where t1.a in
 (
select t2.a
from table2 t2
);

select t1.*
from table1 t1, table2 t2
where t1.a = t2.a;

These 2 queries will produce the same result only if a is a unique key for t2, otherwise the second query can return duplicate rows.

As to performance, it depends on what indexes exist, how many rows etc. However, I'd suspect that the second query would be the most efficient for some data - assuming the queries are equivalent. The first could cause an additional sort on table2 if there is no index on A.

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