单项选择题
A.SELECT &1, "&2" FROM &3 WHERE last_name = '&4';
B.SELECT &1, '&2' FROM &3 WHERE '&last_name = '&4'';
C.SELECT &1, &2 FROM &3 WHERE last_name = '&4';
D.SELECT &1, '&2' FROM EMP WHERE last_name = '&4';
多项选择题 Click the Exhibit button and examine the data in the EMPLOYEES table. Which three subqueries work?（）
单项选择题 Which SQL statement defines a FOREIGN KEY constraint on the DEPTNO column of the EMP table?（）
单项选择题 Click the Exhibit button and examine the data in the EMPLOYEES and DEPARTMENTS tables.You want to retrieve all employees, whether or not they have matching departments in the departments table. Which query would you use?（）