mysql left join join right

my.name = java.name;

+------+------+
| name | name |
+------+------+
| blue | blue |
+------+------+
1 row in set (0.00 sec)查询结果 

2.left join 外联查询 已左表为主表 左表的信息全部会全部查出来 右表的信息只有相关联的才能查出来 剩下的查询结果为null 效率慢一点

select * from java left join mysql as my on java.name=my.name;


+-------+------+
| name  | name |
+-------+------+
| java1 | NULL |
| java2 | NULL |
| blue  | blue |
+-------+------+
3 rows in set (0.00 sec) 查询结果

3.rignt join 正好与left join 相反

mysql left join join right

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