单项选择题
A.Group functions on columns ignore NULL values.
B.Group functions on columns returning dates include NULL values.
C.Group functions on columns returning numbers include NULL values.
D.Group functions on columns cannot be accurately used on columns that contain NULL values.
E.Group functions on columns include NULL values in calculations if you use the keyword INC_NULLS.
多项选择题 Which two statements about sequences are true? （）
单项选择题 The EMP table contains these columns: LAST_NAME VARCHAR2 (25) SALARY NUMBER (6,2) DEPARTMENT_ID NUMBER (6) You need to display the employees who have not been assigned to any department. You write the SELECT statement: SELECT LAST_NAME, SALARY, DEPARTMENT_ID FROM EMP WHERE DEPARTMENT_ID = NULL; What is true about this SQL statement ?（）
单项选择题 Click the Exhibit button to examine the structures of the EMPLOYEES, DEPARTMENTS, and TAX tables. For which situation would you use a nonequijoin query?（）