What are the principles of matching for a union index in DB2?

The matching principle for a combined index in DB2 means that if the columns in the query match the columns in the combined index in the same order and include all columns in the combined index, then the combined index can be used. If the columns in the query do not match the columns in the combined index in the same order or do not include all columns in the combined index, then the combined index will not be used.