You have to pass values as parameters because you cannot make any assumption about work areas that query uses.

SELECT * FROM MyTable WHERE test(DATE1, DATE2) > 10

FUNCTION test(tdDATE1, tdDATE2)
RETURN MAX(tdDATE1 - tdDATE2,0)

>I am experiencing a strange problem with the following code:
>
>

>SELECT * FROM MyTable WHERE test() > 10
>
>FUNCTION test
>RETURN (MAX(MyTable.DATE1-MyTable.DATE2,0))
>

>
>The code above returns (selects) no records if the value after test() is greater than 10 (e.g. test() > 11). However, many records in the table MyTable have value of DATE1 greater than DATE2 by more than even 20.
>
>What am I missing in my sample code above?