Câu 28: C2090-612: DB2 10 DBA for zOS

When defining a foreign key on a table, which statement is true?

1. A. It is not mandatory to have an index on the foreign key columns but it can help to avoid locking problems. — đáp án hiện tại
2. B. There is no need to define an index on the foreign key columns as DB2 cannot use an index for foreign key checking.
3. C. It is not mandatory to have an index on the foreign key columns but it can help performance when you insert rows into this table.
4. D. You must define an index on the foreign key columns where the index columns are the same as the foreign key columns to guarantee uniqueness of the