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?（）

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?（）