Say we have two tables:

tab1  tab2
1          2
2         3
4         4
5

[sql]select t1.col1, t2.col2
from tab1 t1, tab2 t2
where t1.col1 = t2.col2(+) –pl/sql

–Informix SQL: …from tab1 t1, outer tab2 t2[/sql]

Result:
t1 t2
1   –
2   2
4   4
5   –

–this will take primary table tab1 rows and match with tab2, including tab2’s nulls