052-185

User SCOTT executes the following command on the EMP table but has not issued COMMIT,
ROLLBACK, or any data definition language (DDL) command:
SQL> SELECT ename FROM emp
2 WHERE job='CLERK' FOR UPDATE OF empno;
SCOTT has opened another session to work with the database instance. Which three operations would wait when issued in SCOTT's second session? (Choose three.)
A.LOCK TABLE emp IN SHARE MODE;
B.LOCK TABLE emp IN EXCLUSIVE MODE;
C.UPDATE emp SET sal=sal*1.2 WHERE job=MANAGER;
D.INSERT INTO emp(empno,ename) VALUES (1289,'Harry');
E.SELECT ename FROM emp WHERE job='CLERK' FOR UPDATE OF empno;

这个 select ... for update 是在 TX 加上了 S 锁，在 TM 上增加了 SX 锁，
因此不能在 TX 上增加 X 锁，不能在 TM 上增加 S、 SSX、 X 锁
A：正确，这个相当于 TMS 锁
B：正确，这个是 TM 的 X 锁
C：这里只是 TM 的 SX 锁
D：和 C 一样
E：正确，这里是 SX 锁，锁的是不同的记录