mysql 7种JOIN理论，看完你就懂了
Posted 信念0118
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select * from tbl_emp a inner join tbl_dept b on a.deptId=b.id;
select * from tbl_emp a LEFT JOIN tbl_dept b on a.deptId=b.id;
select * from tbl_emp a RIGHT JOIN tbl_dept b on a.deptId=b.id;
select * from tbl_emp a LEFT JOIN tbl_dept b on a.deptId=b.id where b.id is null;
select * from tbl_emp a RIGHT JOIN tbl_dept b on a.deptId=b.id where a.id is null;
select * from tbl_emp a LEFT JOIN tbl_dept b on a.deptId=b.id union select * from tbl_emp a RIGHT JOIN tbl_dept b on a.deptId=b.id;
select * from tbl_emp a LEFT JOIN tbl_dept b on a.deptId=b.id where b.id is null union select * from tbl_emp a RIGHT JOIN tbl_dept b on a.deptId=b.id where a.id is null;
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