Hi,
I have this:
create table a ( x int4 primary key, dat int4, count int4 ) ; create table b ( x int4 references a(x), count int4 ) ;
insert into a values ( 1, 1, 10 ) ; insert into a values ( 2, 2, 20 ) ; insert into b values ( 1, 2 ) ; insert into b
values( 1, 3 ) ; insert into b values ( 2, 3 ); insert into b values ( 2, 4 );
select * from a ; select * from b ;
x | dat | count ---+-----+------- 1 | 1 | 10 2 | 2 | 20 (2 rows)
x | count ---+------- 1 | 2 1 | 3 2 | 3 2 | 4 (4 rows)
select a.x, a.dat, a.count - sum(b.count) from a, b where a.x = b.x group by a.x, a.dat, a.count ;
x | ?column? ---+---------- 1 | 5 2 | 13 (2 rows)
My concern is with the "group by" clause. Strictly speaking, it
shouldn't be necessary to *also* group by a.dat and a.count, since a.x
is a primary key, right? Is there some performance loss in specifying
a.dat and a.count in the group by? Should I be doing this some other
way?
Thanks,
-itai
