多项选择题
A. A single row subquery can retrieve only one column and one row.
B. A single row subquery can retrieve only one row but many columns.
C. A multiple row subquery can retrieve multiple rows and multiple columns.
D. A multiple row subquery can be compared by using the ">" operator.
E. A single row subquery can use the IN operator.
F. A multiple row subquery can use the "=" operator.
单项选择题 In a SELECT statement that includes a WHERE clause, where is the GROUP BY clause placed in the SELECT statement?（）
单项选择题 Examine the data of the EMPLOYEES table. EMPLOYEES (EMPLOYEE_ID is the primary key. MGR_ID is the ID of managers and refers to the EMPLOYEE_ID) Which statement lists the ID, name, and salary of the employee, and the ID and name of the employees manager, for all the employees who have a manager and earn more than 4000?（）
多项选择题 When should you create a role? （）