写了6年SQL，推荐快速上手MySQL 的SQL语句

写了6、7年SQL，有写复杂，有写简单，但总体而言，基础是统一的，。就像编程之需要会加减乘除，用MySQL懂这些SQL就足够了。

目录

• • • [1. SELECT 查询](#1. SELECT 查询)
    • [2. WHERE 子句](#2. WHERE 子句)
    • [3. ORDER BY 子句](#3. ORDER BY 子句)
    • [4. GROUP BY 子句](#4. GROUP BY 子句)
    • [5. HAVING 子句](#5. HAVING 子句)
    • [6. JOIN 查询](#6. JOIN 查询)
    • [7. 子查询](#7. 子查询)
    • [8. INSERT INTO 查询](#8. INSERT INTO 查询)
    • [9. UPDATE 查询](#9. UPDATE 查询)
    • [10. DELETE 查询](#10. DELETE 查询)
    • [11. LIMIT 子句](#11. LIMIT 子句)
    • [12. DISTINCT 关键字](#12. DISTINCT 关键字)

MySQL 查询语句是用于从数据库中检索数据的语句。以下是一些常见的 MySQL 查询语句，并附详细说明和示例：

1. SELECT 查询

基本查询

SELECT column1, column2, ...
FROM table_name;

示例：

SELECT first_name, last_name
FROM employees;

从 employees 表中选择 first_name 和 last_name 字段。

查询所有列

SELECT *
FROM table_name;

示例：

SELECT *
FROM employees;

从 employees 表中选择所有列。

带条件的查询

SELECT column1, column2, ...
FROM table_name
WHERE condition;

示例：

SELECT first_name, last_name
FROM employees
WHERE department = 'Sales';

从 employees 表中选择 Sales 部门的 first_name 和 last_name 字段。

2. WHERE 子句

使用 AND 和 OR 逻辑运算符

SELECT column1, column2, ...
FROM table_name
WHERE condition1 AND condition2 OR condition3;

示例：

SELECT first_name, last_name
FROM employees
WHERE department = 'Sales' AND salary > 50000;

从 employees 表中选择 Sales 部门且薪水大于 50000 的员工的 first_name 和 last_name 字段。

3. ORDER BY 子句

按指定列排序

SELECT column1, column2, ...
FROM table_name
ORDER BY column1 ASC|DESC, column2 ASC|DESC, ...;

示例：

SELECT first_name, last_name
FROM employees
ORDER BY last_name ASC, first_name DESC;

按 last_name 升序和 first_name 降序排列 employees 表中的数据。

4. GROUP BY 子句

按指定列分组并聚合数据

SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1;

示例：

SELECT department, COUNT(*)
FROM employees
GROUP BY department;

按 department 列对 employees 表中的数据进行分组，并计算每个部门的员工数量。

5. HAVING 子句

对分组后的结果进行过滤

SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1
HAVING condition;

示例：

SELECT department, COUNT(*)
FROM employees
GROUP BY department
HAVING COUNT(*) > 5;

筛选出员工数量大于 5 的部门。

6. JOIN 查询

内连接

SELECT columns
FROM table1
INNER JOIN

table2
ON table1.column = table2.column;

示例：

SELECT employees.first_name, employees.last_name, departments.department_name
FROM employees
INNER JOIN departments
ON employees.department_id = departments.department_id;

将 employees 表和 departments 表进行内连接，选择 first_name、last_name 和 department_name。

左连接

SELECT columns
FROM table1
LEFT JOIN table2
ON table1.column = table2.column;

示例：

SELECT employees.first_name, employees.last_name, departments.department_name
FROM employees
LEFT JOIN departments
ON employees.department_id = departments.department_id;

从 employees 表中选择所有记录，并匹配 departments 表中的记录，如果没有匹配到则返回 NULL。

右连接

SELECT columns
FROM table1
RIGHT JOIN table2
ON table1.column = table2.column;

示例：

SELECT employees.first_name, employees.last_name, departments.department_name
FROM employees
RIGHT JOIN departments
ON employees.department_id = departments.department_id;

从 departments 表中选择所有记录，并匹配 employees 表中的记录，如果没有匹配到则返回 NULL。

7. 子查询

在 SELECT 中使用子查询

SELECT column1
FROM table_name
WHERE column2 = (SELECT column
                 FROM another_table
                 WHERE condition);

示例：

SELECT first_name, last_name
FROM employees
WHERE department_id = (SELECT department_id
                       FROM departments
                       WHERE department_name = 'Sales');

从 employees 表中选择 Sales 部门的所有员工。

在 FROM 子句中使用子查询

SELECT subquery.column1, subquery.column2
FROM (SELECT column1, column2
      FROM table_name
      WHERE condition) AS subquery;

示例：

SELECT sub.first_name, sub.last_name
FROM (SELECT first_name, last_name
      FROM employees
      WHERE department_id = 1) AS sub;

从子查询结果中选择 department_id 为 1 的员工的 first_name 和 last_name。

8. INSERT INTO 查询

插入数据

INSERT INTO table_name (column1, column2, column3, ...)
VALUES (value1, value2, value3, ...);

示例：

INSERT INTO employees (first_name, last_name, department_id, salary)
VALUES ('John', 'Doe', 3, 50000);

向 employees 表中插入一条新记录。

9. UPDATE 查询

更新数据

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

示例：

UPDATE employees
SET salary = 55000
WHERE last_name = 'Doe';

更新 last_name 为 'Doe' 的员工的 salary 为 55000。

10. DELETE 查询

删除数据

DELETE FROM table_name
WHERE condition;

示例：

DELETE FROM employees
WHERE last_name = 'Doe';

删除 last_name 为 'Doe' 的员工记录。

11. LIMIT 子句

限制结果集

SELECT column1, column2, ...
FROM table_name
LIMIT number;

示例：

SELECT first_name, last_name
FROM employees
LIMIT 10;

选择前 10 条员工记录。

12. DISTINCT 关键字

去重查询

SELECT DISTINCT column1, column2, ...
FROM table_name;

示例：

SELECT DISTINCT department_id
FROM employees;

选择 employees 表中所有不同的 department_id。

这些示例涵盖了 MySQL 中的基本查询语句及其常见用法。通过这些示例，你可以构建更复杂的查询来满足不同的数据检索需求。