Q: Why the field expression used for making the unique map cannot be relational expression such as "SmID>100" when the dataset for making the unique map is in the datasource whose engine type is oracle, SQL or DB2?

When you use the dataset in the datasource whose engine type is Oracle, SQL or DB2 to make the unique map, if you use the relational expression such as "SmID>100" as the field expression, the operation will fail and return null. Therefore the field expression should be the field name or the arithmetic expression such as "SmID" and "SmID + 1 "