(笔记)MySQL的JOIN所有语句

最新推荐文章于 2025-05-30 10:29:15 发布

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最新推荐文章于 2025-05-30 10:29:15 发布

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分类专栏： MYSQL

本文链接：https://blog.youkuaiyun.com/qq_38056704/article/details/80012621

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本文详细介绍了SQL中不同类型的联结操作，包括内联结、左联结、右联结及全外联结，并通过具体实例展示了如何使用这些联结来查询数据库中的相关记录。

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Join的两个表需要外键才能建立联结，仅仅字段名相同不会建立联结

SELECT *

FROM sgw_dept d INNER JOIN sgw_emp e
ON d.`id` = e.`deptid`

SELECT *
FROM sgw_dept d LEFT JOIN sgw_emp e
ON d.`id` = e.`deptid`

SELECT *
FROM sgw_dept d RIGHT JOIN sgw_emp e
ON d.`id` = e.`deptid`

SELECT *
FROM sgw_dept d LEFT JOIN sgw_emp e
ON d.`id` = e.`deptid`
WHERE e.`deptid` IS NULL

SELECT *
FROM sgw_dept d LEFT JOIN sgw_emp e
ON d.`id` = e.`deptid`
WHERE d.`id` IS NULL

SELECT *
FROM sgw_dept d LEFT JOIN sgw_emp e
ON d.`id` = e.`deptid`
UNION
SELECT *
FROM sgw_dept d RIGHT JOIN sgw_emp e
ON d.`id` = e.`deptid`

SELECT *
FROM sgw_dept d LEFT JOIN sgw_emp e
ON d.`id` = e.`deptid`
WHERE d.`id` IS NULL
UNION
SELECT *
FROM sgw_dept d LEFT JOIN sgw_emp e
ON d.`id` = e.`deptid`
WHERE e.`deptid` IS NULL