MySQL七种JOIN类型小结

        在开始之前，我们创建两个表用于演示将要介绍的其中join类型。

建表

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create table `tbl_dept` (     `id` int (11) not null auto_increment,     `deptname` varchar (30) default null ,     `locadd` varchar (40) default null ,     primary key (`id`) ) engine=innodb auto_increment=1 default charset=utf8;

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create table `tbl_emp` (     `id` int (11) not null auto_increment,     ` name ` varchar (20) default null ,     `deptid` varchar (11) not null ,     primary key (`id`),     key `fk_dept_id` (`deptid`) ) engine=innodb auto_increment=1 default charset=utf8;

初始化数据

七种join

1. a ∩ b

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select < select_list > from tablea a inner join tableb b # 共有 on a. key = b. key

2. a ( = a ∩ b + a* )

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select < select_list > from tablea a left join tableb b on a. key = b. key

3. b ( = a ∩ b + b* )

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select < select_list > from tablea a right join tableb b on a. key = b. key

4. a* ( = a - a ∩ b )

 

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select < select_list > from tablea a left join tableb b on a. key = b. key # on 时主表保留 where b. key is null # 筛选a表数据

5. b* ( = b - a ∩ b )

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select < select_list > from tablea a right join tableb b on a. key = b. key where a. key is null

6. a ∪ b

 

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select < select_list > from tablea a full outer join tableb b ## full outer 仅oracle支持 on a. key = b. key

 

7. a ∪ b - a ∩ b

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select < select_list > from tablea a full outer join tableb b on a. key = b. key where a. key is null or b. key is null

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原文链接：https://blog.csdn.net/qq_51026595/article/details/120895365