A constant expression is any expression that uses transformation functions (except aggregate functions) to write constant expressions. You cannot use values from input, input/output, or variable ports in a constant expression.
Some valid constant expressions include:
500 * 1.75
TO_DATE('January 1, 1998, 12:05 AM','MONTH DD, YYYY, HH:MI AM')
ERROR ('Null not allowed')
ABORT('Null not allowed')
You cannot use values from ports within the expression because the Integration Service assigns default values for the entire mapping when it initializes the session.
The following examples are not valid because they use values from ports:
IN_PRICE * IN_QUANTITY
You cannot call a stored procedure or lookup table from a default value expression.