MySQL - 检查两个值是否相等或均为 NULL

MySQL - 检查两个值是否相等或均为 NULL？

mysql
SELECT *
FROM employees
WHERE first_name IS NULL AND last_name IS NULL;

mysql
SELECT *
FROM employees
WHERE first_name = last_name;

mysql
SELECT *
FROM employees
WHERE (first_name = last_name) OR (first_name IS NULL AND last_name IS NULL);

mysql
-- 创建示例表
CREATE TABLE employees (
  id INT PRIMARY KEY,
  first_name VARCHAR(50),
  last_name VARCHAR(50)
);
-- 插入示例数据
INSERT INTO employees (id, first_name, last_name)
VALUES (1, 'John', 'Doe'),
       (2, NULL, 'Smith'),
       (3, 'Jane', 'Doe'),
       (4, NULL, NULL);