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?（）

单项选择题 Which of the following constraint types can be used to ensure the value of an INTEGER column references only positive values?（）

单项选择题 A view is created with the following statement:CREATE VIEW v1 AS SELECT col1, col2, col3 FROM t1 WHERE col4 > 1000 ; When will DB2 access the data from table T1 for view V1?（）