SQL42 删除emp_no重复的记录，只保留最小的id对应的记录。

描述

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');

 

删除后titles_test表为(注：最后会select * from titles_test表来对比结果)

 

id	emp_no	title	from_date	to_date
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

 

DELETE FROM titles_test WHERE id NOT IN
(   SELECT * FROM (
    SELECT MIN(id) FROM titles_test 
    GROUP BY emp_no
) a );