A little complicated SQL

I want to improve perfomance of my application but database structure is not good.

Here is problemm:

One SQL is:
select A,B from T1;

for each row I have to create another query select C from X1,X2 where X1.A=A and X2.B=B and X1.D=X2.D;

X1.A can be absent, X2.B can be absent and relation X1.D=X2.D can be absent.

So I can have something or nothing.

So right now I have rowset like this

        A B Query C

       A1	B1	select C from X1,X2 where X1.A='A1' and X2.B='B1' and
X1.D=X2.D		C1
       A2	B2	select C from X1,X2 where X1.A='A2' and X2.B='B2' and
X1.D=X2.D		nothing
       A3	B3	select C from X1,X2 where X1.A='A3' and X2.B='B3' and
X1.D=X2.D		C3

Can I create query which returns for me

        A B C

       A1	B1	C1
       A2	B2	null
       A3	B3	C3

in one select statement?
And I can't use PL/SQL in our database :(

Thanks is advance.

Alex Kizub. Received on Thu Jul 18 2002 - 07:39:48 CDT