Re: Questions re subqueries

A NULL will not equate to anything not even NULL, and also a NULL will not NOT equate to anything either. So ...

select count(*) from dual
where NULL = NULL

Will get zero rows

select count(*) from dual
where NULL != NULL

Will get zero rows

Basically you will get a false result using NULLs unless you use the special syntax IS NULL or IS NOT NULL. Also DECODE will allow you to equate NULL.

HTH
Luke

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