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【MySQL】多表查询7种SQL JOIN的实现

2022-08-18 19:02:25 阅读：209 来源： 互联网

标签：JOIN name employee MySQL department 多表 id SELECT

两个表关联有这7种情况
1.内连接
2.左外连接
3.右外连接
4.A-A ∩ B
5.B-A ∩ B
6.满外连接
7.去除交集部分

两个表关联有这7种情况

1.内连接

SELECT employee_id,department_name
FROM employees e JOIN departments d
ON e.`department_id` = d.`department_id`;

2.左外连接

SELECT employee_id,department_name
FROM employees e LEFT JOIN departments d
ON e.`department_id` = d.`department_id`;

3.右外连接

SELECT employee_id,department_name
FROM employees e RIGHT JOIN departments d
ON e.`department_id` = d.`department_id`;

4.A-A ∩ B

SELECT employee_id,department_name
FROM employees e LEFT JOIN departments d
ON e.`department_id` = d.`department_id`
WHERE d.`department_id` IS NULL;

5.B-A ∩ B

SELECT employee_id,department_name
FROM employees e RIGHT JOIN departments d
ON e.`department_id` = d.`department_id`
WHERE e.`department_id` IS NULL;

6.满外连接

两种方式取并集

方式一：

SELECT employee_id,department_name
FROM employees e LEFT JOIN departments d
ON e.`department_id` = d.`department_id`
UNION ALL
SELECT employee_id,department_name
FROM employees e RIGHT JOIN departments d
ON e.`department_id` = d.`department_id`
WHERE e.`department_id` IS NULL;

方式二：

SELECT employee_id,department_name
FROM employees e LEFT JOIN departments d
ON e.`department_id` = d.`department_id`
WHERE d.`department_id` IS NULL
UNION ALL
SELECT employee_id,department_name
FROM employees e RIGHT JOIN departments d
ON e.`department_id` = d.`department_id`;

7.去除交集部分

这两个取并集

SELECT employee_id,department_name
FROM employees e LEFT JOIN departments d
ON e.`department_id` = d.`department_id`
WHERE d.`department_id` IS NULL
UNION ALL
SELECT employee_id,department_name
FROM employees e RIGHT JOIN departments d
ON e.`department_id` = d.`department_id`
WHERE e.`department_id` IS NULL;

标签：JOIN,name,employee,MySQL,department,多表,id,SELECT
来源： https://www.cnblogs.com/zhishu/p/16596451.html

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