MySQL 七种 JOIN
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共有
SELECT
*
FROM
t_dept a
INNER JOIN t_emp b ON a.id = b.deptId;左独占+共有
SELECT
*
FROM
t_dept a
LEFT JOIN t_emp b ON a.id = b.deptId;右独占+共有
SELECT
*
FROM
t_dept a
RIGHT JOIN t_emp b ON a.id = b.deptId;左独占
SELECT
*
FROM
t_dept a
LEFT JOIN t_emp b ON a.id = b.deptId
WHERE b.deptId IS NULL;右独占
SELECT
*
FROM
t_dept a
RIGHT JOIN t_emp b ON a.id = b.deptId
WHERE a.id IS NULL;左右全部
SELECT
*
FROM
t_dept a
LEFT JOIN t_emp b ON a.id = b.deptId
UNION
SELECT
*
FROM
t_dept a
RIGHT JOIN t_emp b ON a.id = b.deptId;左独占+右独占
SELECT
*
FROM
t_dept a
LEFT JOIN t_emp b ON a.id = b.deptId
WHERE b.deptId IS NULL
UNION
SELECT
*
FROM
t_dept a
RIGHT JOIN t_emp b ON a.id = b.deptId
WHERE a.id IS NULL;以上是关于MySQL 七种 JOIN的主要内容，如果未能解决你的问题，请参考以下文章