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  • mysql 数据操作 多表查询 多表连接查询 外链接之左连接 右连接

    1.外链接之左连接:优先显示左表全部记录

     

    left join

    在内连接的基础上保留左表的记录

    即便左表有一条记录和右表没有关系,也把他留下

    mysql> select * from employee left join department on employee.dep_id = department.id;
    +----+------------+--------+------+--------+------+--------------+
    | id | name       | sex    | age  | dep_id | id   | name         |
    +----+------------+--------+------+--------+------+--------------+
    |  1 | mike       | male   |   18 |    200 |  200 | 技术         |
    |  5 | liwenzhou  | male   |   18 |    200 |  200 | 技术         |
    |  2 | alex       | female |   48 |    201 |  201 | 人力资源     |
    |  3 | jack       | male   |   38 |    201 |  201 | 人力资源     |
    |  4 | yuanhao    | female |   28 |    202 |  202 | 销售         |
    |  6 | jingliyang | female |   18 |    204 | NULL | NULL         |
    +----+------------+--------+------+--------+------+--------------+
    6 rows in set (0.00 sec)

    2.外链接之右连接:优先显示右表全部记录

    在内连接的基础上保留右表的记录

    right join

    mysql> select * from employee right join department on employee.dep_id = department.id;
    +------+-----------+--------+------+--------+------+--------------+
    | id   | name      | sex    | age  | dep_id | id   | name         |
    +------+-----------+--------+------+--------+------+--------------+
    |    1 | mike      | male   |   18 |    200 |  200 | 技术         |
    |    2 | alex      | female |   48 |    201 |  201 | 人力资源     |
    |    3 | jack      | male   |   38 |    201 |  201 | 人力资源     |
    |    4 | yuanhao   | female |   28 |    202 |  202 | 销售         |
    |    5 | liwenzhou | male   |   18 |    200 |  200 | 技术         |
    | NULL | NULL      | NULL   | NULL |   NULL |  203 | 运营         |
    +------+-----------+--------+------+--------+------+--------------+
    6 rows in set (0.00 sec)
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  • 原文地址:https://www.cnblogs.com/mingerlcm/p/9893180.html
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