单项选择题
A.must contain unique values.
B.cannot be CAST to other data types.
C.is created using the CREATE DISTINCT command.
D.contains a value that was automatically calculated from values in other columns.
单项选择题 Which of the following DB2 data types has a fixed length?（）
单项选择题 Which of the following actions may cause a trigger to be fired?（）
单项选择题 What type of constraint is used to ensure that each row inserted into the EMPLOYEE table with a value in the WORKDEPT column has a row with a corresponding value in the DEPTNO column of the DEPARTMENT table?（）