SQL练习43：将所有to_date为9999-01-01的全部更新为NULL,且 from_date更新为2001-01-01

题目链接：牛客网

题目描述
将所有to_date为9999-01-01的全部更新为NULL,且 from_date更新为2001-01-01。

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');

更新后的值:
titles_test 表的值：

id	emp_no	title	from_date	to_date
1	10001	Senior Engineer	2001-01-01	NULL
2	10002	Staff	2001-01-01	NULL
3	10003	Senior Engineer	2001-01-01	NULL
4	10004	Senior Engineer	2001-01-01	NULL
5	10001	Senior Engineer	2001-01-01	NULL
6	10002	Staff	2001-01-01	NULL
7	10003	Senior Engineer	2001-01-01	NULL

解法
使用UPDATE 表名 SET ... WHERE ...进行更新操作，注意：SET中语句用逗号分隔。

UPDATE titles_test
SET to_date = NULL, from_date = '2001-01-01'
WHERE to_date = '9999-01-01'