53題、choose two
The HR user executes the following query on the EMPLOYEES table but does not issue COMMIT, ROLLBACK, or any data definition language (DDL) command after that:
SQL> SELECT job
FROM employees
WHERE job='CLERK' FOR UPDATE OF empno;
HR then opens a second session.
Which two operations wait when executed in HR'S second session?
A) SELECT job FROM employees WHERE job='CLERK' FOR UPDATE OF empno;
B) INSERT INTO employees(empno,ename,job) VALUES (2001,'Harry','CLERK');
C) SELECT empno,ename FROM employees WHERE job='CLERK';
D) INSERT INTO employees(empno,ename) VALUES (1289,'Dick');
E) LOCK TABLE employees IN EXCLUSIVE MODE;
Answer:AE
(解析:因爲查詢中用到了for update of,那麼被查詢到的行會被加鎖,所以A答案會造成等待,E答案因爲要鎖整個表,所以也要發生等待。來自3組:1015267481)