When a table function with dynamic result row specification is defined by the CREATE FUNCTION statement, the RETURNS TABLE VARYING COLUMNS specifies the maximum number of result columns that the table function supports.
The actual number and definition (data type and attributes) of the output columns that the table function must return is not known until runtime, when the table function is invoked in a SELECT statement.
A table function uses FNC_TblGetColDef at runtime to get the number and definition of the output columns that the table function must return.
This function can be called during any table function processing phase.
This function can only be called from within a table function. Calling this function from an external stored procedure, scalar UDM, scalar function, or aggregate function results in an exception on the transaction.