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MySQL之表连接-> 内连接，左外连接，右外链接，全连接

1、首先创建student库

create database student;

2、在数据库中创建boy表和 girl表，

mysql> create table boy(
    ->  boyId int primary key auto_increment,
    -> boyName varchar(100) not null,
    -> age int,
    -> connectId int)
    -> auto_increment = 1;

mysql> create table girl(
    -> girlid int primary key auto_increment,
    -> girlName varchar(100) not null,
    -> age int,
    -> connectId int)
    -> auto_increment = 101;

① 对boy表插入部分数据

mysql> insert into boy(boyName,age) values('李易峰',30);
mysql> insert into boy(boyName,age) values('吴奇隆',40);
mysql> insert into boy(boyName,age) values('周润发',55);
mysql> insert into boy(boyName,age) values('周星驰',45);
mysql> insert into boy(boyName,age) values('刘德华',47);
mysql> insert into boy(boyName,age) values('成龙',60);

mysql> select * from boy;
+-------+---------+-----+-----------+
| boyId | boyName | age | connectId |
+-------+---------+-----+-----------+
|     1 | 李易峰  |  30 | NULL      |
|     2 | 吴奇隆  |  40 | NULL      |
|     3 | 周润发  |  55 | NULL      |
|     4 | 周星驰  |  45 | NULL      |
|     5 | 刘德华  |  47 | NULL      |
|     6 | 成龙    |  60 | NULL      |
+-------+---------+-----+-----------+

② 对girl表插入部分数据

mysql> insert into girl(girlName,age) values('刘亦菲',31);
mysql> insert into girl(girlName,age) values('唐嫣',35);
mysql> insert into girl(girlName,age) values('刘诗诗',38);
mysql> insert into girl(girlName,age) values('马苏',30);
mysql> insert into girl(girlName,age) values('杨幂',39);
mysql> insert into girl(girlName,age) values('赵丽颖',29);

mysql> select * from girl;
+--------+----------+-----+-----------+
| girlid | girlName | age | connectId |
+--------+----------+-----+-----------+
|    101 | 刘亦菲   |  31 | NULL      |
|    102 | 唐嫣     |  35 | NULL      |
|    103 | 刘诗诗   |  38 | NULL      |
|    104 | 马苏     |  30 | NULL      |
|    105 | 杨幂     |  39 | NULL      |
|    106 | 赵丽颖   |  29 | NULL      |
+--------+----------+-----+-----------+

3、修改表中的connectId，利用boy表中的boyId 连接girl表中的girlId

① boyId=2 连接 girlId = 102

mysql> update boy set connectId=102 where boyId=2;

② boyId=3 连接 girlId = 104

mysql> update boy set connectId=104 where boyId=3;

③ boyId=6 连接 girlId = 105

mysql> update boy set connectId=105 where boyId=6;

得出boy表

mysql> select * from boy;
+-------+---------+-----+-----------+
| boyId | boyName | age | connectId |
+-------+---------+-----+-----------+
|     1 | 李易峰  |  30 | NULL      |
|     2 | 吴奇隆  |  40 |       102 |
|     3 | 周润发  |  55 |       104 |
|     4 | 周星驰  |  45 | NULL      |
|     5 | 刘德华  |  47 | NULL      |
|     6 | 成龙    |  60 |       105 |
+-------+---------+-----+-----------+

4、修改表中的connectId，利用girl表中的girlId 连接boy表中的boyId

① girlId=101 连接 boyd = 3

mysql> update girl set connectId=3 where girlId=101;

② girlId=103 连接 boyd = 4

mysql> update girl set connectId=4 where girlId=103;

③ girlId=105 连接 boyd = 6

update girl set connectId=6 where girlId=105;

得出girl表

mysql> select * from girl;
+--------+----------+-----+-----------+
| girlid | girlName | age | connectId |
+--------+----------+-----+-----------+
|    101 | 刘亦菲   |  31 |         3 |
|    102 | 唐嫣     |  35 | NULL      |
|    103 | 刘诗诗   |  38 |         4 |
|    104 | 马苏     |  30 | NULL      |
|    105 | 杨幂     |  39 |         6 |
|    106 | 赵丽颖   |  29 | NULL      |
+--------+----------+-----+-----------+

5、连接，分为内连接、左连接、有连接， where形式连接

① where连接，匹配的数据显示出来

　　boy表连接girl表

mysql> select b.*,g.*
    -> from boy b,girl g
    -> where b.connectId = g.girlId;
+-------+---------+-----+-----------+--------+----------+-----+-----------+
| boyId | boyName | age | connectId | girlid | girlName | age | connectId |
+-------+---------+-----+-----------+--------+----------+-----+-----------+
|     2 | 吴奇隆  |  40 |       102 |    102 | 唐嫣     |  35 | NULL      |
|     3 | 周润发  |  55 |       104 |    104 | 马苏     |  30 | NULL      |
|     6 | 成龙    |  60 |       105 |    105 | 杨幂     |  39 |         6 |
+-------+---------+-----+-----------+--------+----------+-----+-----------+
3 rows in set

　　girl表连接boy表

mysql> select b.*,g.*
    -> from boy b,girl g
    -> where g.connectId = b.boyId;
+-------+---------+-----+-----------+--------+----------+-----+-----------+
| boyId | boyName | age | connectId | girlid | girlName | age | connectId |
+-------+---------+-----+-----------+--------+----------+-----+-----------+
|     3 | 周润发  |  55 |       104 |    101 | 刘亦菲   |  31 |         3 |
|     4 | 周星驰  |  45 | NULL      |    103 | 刘诗诗   |  38 |         4 |
|     6 | 成龙    |  60 |       105 |    105 | 杨幂     |  39 |         6 |
+-------+---------+-----+-----------+--------+----------+-----+-----------+

② 内连接，匹配的显示出来

　　boy - > girl

mysql> select b.*,g.*
    -> from boy b inner join girl g
    -> on b.connectId = g.girlId;
+-------+---------+-----+-----------+--------+----------+-----+-----------+
| boyId | boyName | age | connectId | girlid | girlName | age | connectId |
+-------+---------+-----+-----------+--------+----------+-----+-----------+
|     2 | 吴奇隆  |  40 |       102 |    102 | 唐嫣     |  35 | NULL      |
|     3 | 周润发  |  55 |       104 |    104 | 马苏     |  30 | NULL      |
|     6 | 成龙    |  60 |       105 |    105 | 杨幂     |  39 |         6 |
+-------+---------+-----+-----------+--------+----------+-----+-----------+

　　girl - > boy

mysql> select b.*,g.*
    -> from girl g inner join boy b
    -> on g.connectId = b.boyId;
+-------+---------+-----+-----------+--------+----------+-----+-----------+
| boyId | boyName | age | connectId | girlid | girlName | age | connectId |
+-------+---------+-----+-----------+--------+----------+-----+-----------+
|     3 | 周润发  |  55 |       104 |    101 | 刘亦菲   |  31 |         3 |
|     4 | 周星驰  |  45 | NULL      |    103 | 刘诗诗   |  38 |         4 |
|     6 | 成龙    |  60 |       105 |    105 | 杨幂     |  39 |         6 |
+-------+---------+-----+-----------+--------+----------+-----+-----------+

③ 左外连接 left join on ，哪个表在左边就偏向哪个表，把该表的数据全部列出来，不管匹配不匹配都显示

mysql>  select b.*,g.*
    -> from boy b left join girl g
    -> on b.connectId = g.girlId;
+-------+---------+-----+-----------+--------+----------+------+-----------+
| boyId | boyName | age | connectId | girlid | girlName | age  | connectId |
+-------+---------+-----+-----------+--------+----------+------+-----------+
|     1 | 李易峰  |  30 | NULL      | NULL   | NULL     | NULL | NULL      |
|     2 | 吴奇隆  |  40 |       102 |    102 | 唐嫣     |   35 | NULL      |
|     3 | 周润发  |  55 |       104 |    104 | 马苏     |   30 | NULL      |
|     4 | 周星驰  |  45 | NULL      | NULL   | NULL     | NULL | NULL      |
|     5 | 刘德华  |  47 | NULL      | NULL   | NULL     | NULL | NULL      |
|     6 | 成龙    |  60 |       105 |    105 | 杨幂     |   39 |         6 |
+-------+---------+-----+-----------+--------+----------+------+-----------+

④ 右外连接 right join on ，哪个表在右边就偏向哪个表，把该表的数据全部列出来，不管匹配不匹配都显示

mysql>  select b.*,g.*
    -> from boy b right join girl g
    -> on b.connectId = g.girlId;
+-------+---------+------+-----------+--------+----------+-----+-----------+
| boyId | boyName | age  | connectId | girlid | girlName | age | connectId |
+-------+---------+------+-----------+--------+----------+-----+-----------+
|     2 | 吴奇隆  |   40 |       102 |    102 | 唐嫣     |  35 | NULL      |
|     3 | 周润发  |   55 |       104 |    104 | 马苏     |  30 | NULL      |
|     6 | 成龙    |   60 |       105 |    105 | 杨幂     |  39 |         6 |
| NULL  | NULL    | NULL | NULL      |    101 | 刘亦菲   |  31 |         3 |
| NULL  | NULL    | NULL | NULL      |    103 | 刘诗诗   |  38 |         4 |
| NULL  | NULL    | NULL | NULL      |    106 | 赵丽颖   |  29 | NULL      |
+-------+---------+------+-----------+--------+----------+-----+-----------+

⑤ 全连接（笛卡尔积），MySQL不支持 full join，但是可以通过 union来实现连接结果集(剔除重复数据)，会显示两张表的各自匹配的数据，union all 不会剔除重复数据

mysql> select b.*,g.*
    -> from boy b left join girl g
    -> on b.connectId = g.girlId
    -> union
    -> select b.*,g.*
    -> from boy b right join girl g
    -> on b.connectId = g.girlId;
+-------+---------+------+-----------+--------+----------+------+-----------+
| boyId | boyName | age  | connectId | girlid | girlName | age  | connectId |
+-------+---------+------+-----------+--------+----------+------+-----------+
|     1 | 李易峰  |   30 | NULL      | NULL   | NULL     | NULL | NULL      |
|     2 | 吴奇隆  |   40 |       102 |    102 | 唐嫣     |   35 | NULL      |
|     3 | 周润发  |   55 |       104 |    104 | 马苏     |   30 | NULL      |
|     4 | 周星驰  |   45 | NULL      | NULL   | NULL     | NULL | NULL      |
|     5 | 刘德华  |   47 | NULL      | NULL   | NULL     | NULL | NULL      |
|     6 | 成龙    |   60 |       105 |    105 | 杨幂     |   39 |         6 |
| NULL  | NULL    | NULL | NULL      |    101 | 刘亦菲   |   31 |         3 |
| NULL  | NULL    | NULL | NULL      |    103 | 刘诗诗   |   38 |         4 |
| NULL  | NULL    | NULL | NULL      |    106 | 赵丽颖   |   29 | NULL      |
+-------+---------+------+-----------+--------+----------+------+-----------+

2018年1月16日02:12:02，睡觉...

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原文地址：https://www.cnblogs.com/jpfss/p/11244770.html