self join

Hi,

This probably reflects my confusion with how self joins work.

Suppose we have this table:

=# SELECT * FROM tmp;
a | b
---+---
1 | 2
2 | 3
4 | 5
(3 rows)

If I want to get a table with records where none of the values in column
b are found in column a, I thought this should do it:

=# SELECT * FROM tmp t1, tmp t2 WHERE t2.b <> t1.a;
a | b | a | b
---+---+---+---
1 | 2 | 1 | 2
1 | 2 | 2 | 3
1 | 2 | 4 | 5
2 | 3 | 2 | 3
2 | 3 | 4 | 5
4 | 5 | 1 | 2
4 | 5 | 2 | 3
4 | 5 | 4 | 5
(8 rows)

I need to get:

a | b | a | b
---+---+---+---
1 | 2 | 1 | 2
4 | 5 | 4 | 5

Or just:

a | b
---+---
1 | 2
4 | 5

--
Seb