53题、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：因为查询中用到了for update of，那么被查询到的行会被加锁，所以A答案会造成等待，E答案因为要锁整个表，所以也要发生等待。来自3组：1015267481)
原文地址：https://www.cnblogs.com/cnblogs5359/p/11096403.html