Antw: Outer Joins

>>> "Marc Rohloff" <Marc(dot)Rohloff(at)eskom(dot)co(dot)za> 01.11.2000 09.02 Uhr >>>
>
> select a.col1, b.col2 from a,b
> where a.col1 = b.col2
> or b.col2 is null
>

This query has nothing to do with an outer join. See the following example:

table a

c1
---
x
y

and

table b

c2
---
x

Then an outer join gives:

select a,c1, b.c2
from a left outer join b on a.c1 = b.c2

c1 | c2
x | x
y | (null)

but your query gives:

select a.c1, b.c2
from a, b
where a.c1 = b.c2
or b.c2 is null

c1 | c2
x | x

because there are no rows in table b with c2 is null

-------------
Gerhard