Ignore where clauses when the value is space

Hi,

I have a SQL Select on say a table A that has columns a1 a2 and a3. I am writing a stored procedure that would return a sum of a3 for a specific a1 and a2 values.

So the query looks like this

select sum(a3) from A where a1 = :val1 and a2 = :val2 (val1 and val2 are the in parameters for my stored proc).

Now the issue is I want the where condition to be ignored if val1/val2 is null or space. so if val1 is space, then only the a2 = :val2 condn should be considered and vice versa.

Regards,

Anusha