MySQL的UPDATE或DELETE中子查询不能为同一张表

删除emp_no重复的记录，只保留最小的id对应的记录。
CREATE TABLE IF NOT EXISTS titles_test (
id int(11) not null primary key,
emp_no int(11) NOT NULL,
title varchar(50) NOT NULL,
from_date date NOT NULL,
to_date date DEFAULT NULL);

insert into titles_test values ('1', '10001', 'Senior Engineer', '1986-06-26', '9999-01-01'),
('2', '10002', 'Staff', '1996-08-03', '9999-01-01'),
('3', '10003', 'Senior Engineer', '1995-12-03', '9999-01-01'),
('4', '10004', 'Senior Engineer', '1995-12-03', '9999-01-01'),
('5', '10001', 'Senior Engineer', '1986-06-26', '9999-01-01'),
('6', '10002', 'Staff', '1996-08-03', '9999-01-01'),

('7', '10003', 'Senior Engineer', '1995-12-03', '9999-01-01');

 

错误答案：

delete from titles_test t
where t.id not in
(select min(ti.id) from titles_test ti group by ti.emp_no)

正确答案：

delete from titles_test t
where t.id not in
(select * from(select min(ti.id) from titles_test ti group by ti.emp_no)as a)

另一题，因为子查询中的表和外表不一样，所以可以这么写

update salaries set salary=salary*1.1
where salaries.emp_no in (select emp_no from emp_bonus)
and salaries.to_date='9999-01-01'