【387天】我爱刷题系列146（2018.02.27）

@(一只心中无码的程序员)专栏

叨叨两句

1. ~

SQL习题041

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');

用 UPDATE 语句更新若干列的最基本用法，详细可参考：
http://www.w3school.com.cn/sql/sql_update.asp
https://www.w3schools.com/sql/sql_update.asp
另外要注意若干列 to_date = NULL 和 from_date = '2001-01-01' 之间只能用逗号连接，切勿用 AND 连接。

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