mysql order by，先为null，后为DESC

在MySQL中，使用"ORDER BY"子句可以对查询结果进行排序。通过指定排序字段和排序方式，我们可以按照特定的顺序呈现数据。在本文中，我们将重点介绍如何通过"ORDER BY"子句实现将NULL值排在前面，并按照降序进行排序的功能。

sql
SELECT * FROM employees WHERE salary IS NULL
UNION
SELECT * FROM employees WHERE salary IS NOT NULL ORDER BY salary DESC;

sql
-- 创建员工表
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  salary INT
);
-- 插入示例数据
INSERT INTO employees (id, name, salary) VALUES
  (1, '张三', 5000),
  (2, '李四', 6000),
  (3, '王五', NULL),
  (4, '赵六', 5500),
  (5, '刘七', NULL);
-- 查询并排序
SELECT * FROM employees WHERE salary IS NULL
UNION
SELECT * FROM employees WHERE salary IS NOT NULL ORDER BY salary DESC;

sql
SELECT * FROM products ORDER BY price DESC;

sql
-- 创建产品表
CREATE TABLE products (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  price DECIMAL(10, 2)
);
-- 插入示例数据
INSERT INTO products (id, name, price) VALUES
  (1, '手机', 1999.99),
  (2, '电视', 2999.99),
  (3, '电脑', 3999.99),
  (4, '平板', 1499.99),
  (5, '耳机', 99.99);
-- 查询并排序
SELECT * FROM products ORDER BY price DESC;