SQL43 将所有to_date为9999-01-01的全部更新为NULL SQL43 将所有to_date为9999-01-01的全部更新为NULL

1. 题目

• 题目来源：SQL43 将所有to_date为9999-01-01的全部更新为NULL

• 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。

• 一张表

  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'); 
  

• 所需结果
  

2. 题解

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

关于NULL的用法：

• 可以拿来赋值，a = NULL
• 可使用 IS、IS NOT NULL