This will give the first non-null date.
Syntax: coalesce (date1, date2,
date3 … daten)
Ex:
SQL> select coalesce('12-jan-90','13-jan-99'),
coalesce(null,'12-jan-90','23-mar-
98',null) from dual;
COALESCE(
COALESCE(
------------- ------------
12-jan-90 12-jan-90
