数据库练习

       AND (SAL > 5000 OR SAL<1000);

23 What is the command to add primary key constraint to EMPNO

       ALTER TABLE EMP_2014170165 ADD PRIMARY KEY(EMPNO);

24 What is the command to add a new column EMP_family_name to existing EMP table

       ALTER TABLE EMP_2014170165 

       ADD EMP_family_name VARCHAR2(10);

25 How to drop primary key constraint for EMPNO

       ALTER TABLE EMP_2014170165 

       DROP PRIMARY KEY;

26 rename EMP table to EMPLOYEE

       RENAME EMP_2014170165

       TO EMPLOYEE_2014170165;

27 rename EMPLOYEE  back to EMP

       RENAME EMPLOYEE_2014170165

       TO EMP_2014170165;

28 What is the SQL command to remove column EMP_family_name from EMP table

       ALTER TABLE EMP_2014170165

       DROP COLUMN EMP_family_name;

29 What is the SQL command to copy emp table to employee table

       CREATE TABLE EMPLOYEE_2014170165 AS

       SELECT * FROM EMP_2014170165;

30 What is the SQL command to drop employee table

       DROP TABLE EMPLOYEE_2014170165;

31 What is the SQL command to display name’s of employee entered interactively from user

       SELECT * FROM EMP_2014170165

       WHERE ENAME = ‘&ENTER‘;

32 What is the SQL command to find the employee whose commission is NULL

       SELECT * FROM EMP_2014170165 WHERE COMM IS NULL;

数据库练习

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