query needed very urg.

Hi all,
Please tell me query for following conditions:

Conditions are:

1. a=12, b=3, n=7
2. a=12, b=3, n=NULL
3. a=12, b=NULL, n=NULL

if 1 is true, I don't need any record of 2 or 3. But if it is false then
I need all record of 2, but if 1 and 2 both are wrong then only I need 3. Received on Thu Dec 14 2006 - 01:23:19 CST