浅谈MySQL数据库多表查询【MySQL教程】,MySQL

本篇文章和人人一同相识一下MySQL数据库多表查询。有肯定的参考价值，有须要的朋侪能够参考一下，愿望对人人有所协助。

多表查询

查询结果来自于多张表，即多表查询

子查询：在SQL语句嵌套着查询语句，机能较差，基于某语句的查询结果再次举行的查询
团结查询：UNION
交织衔接：笛卡尔乘积
内衔接：
等值衔接：让表之间的字段以“等值”竖立衔接关联
不等值衔接:不等值衔接查询就是无条件推断，若查询多个表内的数据，个中的数据不会同步，各自把各自的展示出来，没有任何关联。
天然衔接:去掉反复列的等值衔接
外衔接：
左外衔接：FROM tb1 LEFT JOIN tb2 ON tb1.col=tb2.col
右外衔接：FROM tb1 RIGHT JOIN tb2 ON tb1.col=tb2.col
自衔接：本表和本表举行衔接查询

子查询

常用在WHERE子句中的子查询

1、用于比较表达式中的子查询；子查询仅能返回单个值(查询s1表中大于平均岁数的人)

MariaDB [hellodb]> select * from s1 where age > (select avg(age) from s1);
+-------+--------------+-------+-----+--------+---------+-----------+
| StuID | Name         | phone | Age | Gender | ClassID | TeacherID |
+-------+--------------+-------+-----+--------+---------+-----------+
|     3 | Xie Yanke    |  NULL |  53 | M      |       2 |        16 |
|     4 | Ding Dian    |  NULL |  32 | M      |       4 |         4 |
|     5 | Yu Yutong    |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing     |  NULL |  46 | M      |       5 |      NULL |
|    13 | Tian Boguang |  NULL |  33 | M      |       2 |      NULL |
|    24 | Xu Xian      |  NULL |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng  |  NULL | 100 | M      |    NULL |      NULL |
+-------+--------------+-------+-----+--------+---------+-----------+
7 rows in set (0.01 sec)

2、查询结果嵌入到另一个内外,小数转换整数会四舍五入

MariaDB [hellodb]> select avg(age) from s1 ;  (检察s1表平均岁数)
+----------+
| avg(age) |
+----------+
|  25.0857 |
+----------+
1 row in set (0.00 sec)
MariaDB [hellodb]> select * from teachers;  （本来的表内容）
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  26 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

MariaDB [hellodb]> update teachers set age=(select avg(age) from s1); （插进去查询结果的表内容，没有指定字段会改掉一切）
Query OK, 4 rows affected (0.00 sec)
Rows matched: 4  Changed: 4  Warnings: 0

MariaDB [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  25 | M      |
|   2 | Zhang Sanfeng |  25 | M      |
|   3 | Miejue Shitai |  25 | F      |
|   4 | Lin Chaoying  |  25 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

MariaDB [hellodb]> update teachers set age=48 where tid=4;  （把tid为4的age修正成48做下面试验用）
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  25 | M      |
|   2 | Zhang Sanfeng |  25 | M      |
|   3 | Miejue Shitai |  25 | F      |
|   4 | Lin Chaoying  |  48 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

MariaDB [hellodb]> update teachers set age=(select avg(age) from s1) where tid=4;  （指定tid为4的age字段修正）
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  25 | M      |
|   2 | Zhang Sanfeng |  25 | M      |
|   3 | Miejue Shitai |  25 | F      |
|   4 | Lin Chaoying  |  25 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

多表查询:

用子轮回检察s1表，显现teachers表岁数大于s1表平均岁数的人的信息。

MariaDB [hellodb]> update teachers set age=45 where tid=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [hellodb]> update teachers set age=94 where tid=2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [hellodb]> update teachers set age=77 where tid=3;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [hellodb]> select  * from teachers;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  25 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)
（以上是把岁数修正返来做试验）


MariaDB [hellodb]> select * from teachers where age > (select avg(age) from s1);  （多表子轮回查询平均岁数大于25的人）
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
+-----+---------------+-----+--------+
3 rows in set (0.00 sec)

MariaDB [hellodb]> update teachers set age=26 where tid=4;  （修正一下末了一条的岁数为26）
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [hellodb]> select * from teachers where age > (select avg(age) from s1);   （末了一条也大于25就显现出来了）
+-----+---------------+-----+--------+ 
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  26 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

团结查询

union 纵向兼并两张表，表头来自第一条查询纪录.

MariaDB [hellodb]> select * from teachers
    -> union
    -> select stuid,name,age,gender from s1;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  26 | F      |
|   1 | Shi Zhongyu   |  22 | M      |
|   2 | Shi Potian    |  22 | M      |
|   3 | Xie Yanke     |  53 | M      |
|   4 | Ding Dian     |  32 | M      |
|   5 | Yu Yutong     |  26 | M      |
|   6 | Shi Qing      |  46 | M      |
|   7 | Xi Ren        |  19 | F      |
|   8 | Lin Daiyu     |  17 | F      |
|   9 | Ren Yingying  |  20 | F      |
|  10 | Yue Lingshan  |  19 | F      |
|  11 | Yuan Chengzhi |  23 | M      |
|  12 | Wen Qingqing  |  19 | F      |
|  13 | Tian Boguang  |  33 | M      |
|  14 | Lu Wushuang   |  17 | F      |
|  15 | Duan Yu       |  19 | M      |
|  16 | Xu Zhu        |  21 | M      |
|  17 | Lin Chong     |  25 | M      |
|  18 | Hua Rong      |  23 | M      |
|  19 | Xue Baochai   |  18 | F      |
|  20 | Diao Chan     |  19 | F      |
|  21 | Huang Yueying |  22 | F      |
|  22 | Xiao Qiao     |  20 | F      |
|  23 | Ma Chao       |  23 | M      |
|  24 | Xu Xian       |  27 | M      |
|  25 | Sun Dasheng   | 100 | M      |
|  26 | xietingfeng   |  23 | M      |
|  27 | liudehua      |  18 | F      |
|  28 | mahuateng     |  20 | M      |
|  29 | wuyanzu       |  19 | M      |
|  30 | wuzetian      |  21 | F      |
|  31 | Song Jiang    |  18 | M      |
|  32 | Zhang Sanfeng |  18 | M      |
|  33 | Miejue Shitai |  18 | F      |
|  34 | Lin Chaoying  |  18 | F      |
|  38 | abc           |  20 | M      |
+-----+---------------+-----+--------+
39 rows in set (0.00 sec)


MariaDB [hellodb]> select tid as id ,name,age,gender from teachers union select stuid,name,age,gender from s1;  (起一般号替换掉表头的tid并纵向兼并两张表)
+----+---------------+-----+--------+
| id | name          | age | gender |
+----+---------------+-----+--------+
|  1 | Song Jiang    |  45 | M      |
|  2 | Zhang Sanfeng |  94 | M      |
|  3 | Miejue Shitai |  77 | F      |
|  4 | Lin Chaoying  |  26 | F      |
|  1 | Shi Zhongyu   |  22 | M      |
|  2 | Shi Potian    |  22 | M      |
|  3 | Xie Yanke     |  53 | M      |
|  4 | Ding Dian     |  32 | M      |
|  5 | Yu Yutong     |  26 | M      |
|  6 | Shi Qing      |  46 | M      |
|  7 | Xi Ren        |  19 | F      |
|  8 | Lin Daiyu     |  17 | F      |
|  9 | Ren Yingying  |  20 | F      |
| 10 | Yue Lingshan  |  19 | F      |
| 11 | Yuan Chengzhi |  23 | M      |
| 12 | Wen Qingqing  |  19 | F      |
| 13 | Tian Boguang  |  33 | M      |
| 14 | Lu Wushuang   |  17 | F      |
| 15 | Duan Yu       |  19 | M      |
| 16 | Xu Zhu        |  21 | M      |
| 17 | Lin Chong     |  25 | M      |
| 18 | Hua Rong      |  23 | M      |
| 19 | Xue Baochai   |  18 | F      |
| 20 | Diao Chan     |  19 | F      |
| 21 | Huang Yueying |  22 | F      |
| 22 | Xiao Qiao     |  20 | F      |
| 23 | Ma Chao       |  23 | M      |
| 24 | Xu Xian       |  27 | M      |
| 25 | Sun Dasheng   | 100 | M      |
| 26 | xietingfeng   |  23 | M      |
| 27 | liudehua      |  18 | F      |
| 28 | mahuateng     |  20 | M      |
| 29 | wuyanzu       |  19 | M      |
| 30 | wuzetian      |  21 | F      |
| 31 | Song Jiang    |  18 | M      |
| 32 | Zhang Sanfeng |  18 | M      |
| 33 | Miejue Shitai |  18 | F      |
| 34 | Lin Chaoying  |  18 | F      |
| 38 | abc           |  20 | M      |
+----+---------------+-----+--------+
39 rows in set (0.00 sec)

union 本身和本身相连能够去重。

MariaDB [hellodb]> create table t2 select * from teachers;  （先导一张表出来做试验不能有主键，所以只用了这类要领导了数据没有把主键导过来）
Query OK, 4 rows affected (0.01 sec)
Records: 4  Duplicates: 0  Warnings: 0

MariaDB [hellodb]> select * from t2;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  26 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

MariaDB [hellodb]> desc t2;
+--------+----------------------+------+-----+---------+-------+
| Field  | Type                 | Null | Key | Default | Extra |
+--------+----------------------+------+-----+---------+-------+
| TID    | smallint(5) unsigned | NO   |     | 0       |       |
| Name   | varchar(100)         | NO   |     | NULL    |       |
| Age    | tinyint(3) unsigned  | NO   |     | NULL    |       |
| Gender | enum('F','M')        | YES  |     | NULL    |       |
+--------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

（增加反复的行做试验）
MariaDB [hellodb]> insert into t2 set tid=4,name='linchaoying',age=26,gender='F';  （这条纪录增加的只要name不一样少了个空格）
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> insert into t2 set tid=4,name='lin chaoying',age=26,gender='F';  （完整一样加了一行）
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> select * from t2;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  26 | F      |
|   4 | linchaoying   |  26 | F      |
|   4 | lin chaoying  |  26 | F      |
+-----+---------------+-----+--------+
6 rows in set (0.00 sec)

MariaDB [hellodb]> select * from t2 union select * from t2;  （用union过滤掉反复的行，少一个空格的那条纪录过滤不了）
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  26 | F      |
|   4 | linchaoying   |  26 | F      |
+-----+---------------+-----+--------+
5 rows in set (0.00 sec)

运用all 简朴衔接两张表不去重

MariaDB [hellodb]> select * from t2 union all select * from t2;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  26 | F      |
|   4 | linchaoying   |  26 | F      |
|   4 | lin chaoying  |  26 | F      |
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  26 | F      |
|   4 | linchaoying   |  26 | F      |
|   4 | lin chaoying  |  26 | F      |
+-----+---------------+-----+--------+
12 rows in set (0.00 sec)

交织衔接

两张表横向组合，类似于笛卡尔乘积。  （cross join）

两张表运用交织衔接就是这张表的每一行去和另一张表的一切行组合一遍，构成新的行。

MariaDB [hellodb]> select * from s1 cross join teachers;
+-------+---------------+-------+-----+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID | TID | Name          | Age | Gender |
+-------+---------------+-------+-----+--------+---------+-----------+-----+---------------+-----+--------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |   1 | Song Jiang    |  25 | M      |
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |   2 | Zhang Sanfeng |  25 | M      |
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |   3 | Miejue Shitai |  25 | F      |
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |   4 | Lin Chaoying  |  25 | F      |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |   1 | Song Jiang    |  25 | M      |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |   2 | Zhang Sanfeng |  25 | M      |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |   3 | Miejue Shitai |  25 | F      |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |   4 | Lin Chaoying  |  25 | F      |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |   1 | Song Jiang    |  25 | M      |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |   2 | Zhang Sanfeng |  25 | M      |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |   3 | Miejue Shitai |  25 | F      |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |   4 | Lin Chaoying  |  25 | F      |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |   1 | Song Jiang    |  25 | M      |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |   2 | Zhang Sanfeng |  25 | M      |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |   3 | Miejue Shitai |  25 | F      |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |   4 | Lin Chaoying  |  25 | F      |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |   1 | Song Jiang    |  25 | M      |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |   2 | Zhang Sanfeng |  25 | M      |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |   3 | Miejue Shitai |  25 | F      |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |   4 | Lin Chaoying  |  25 | F      |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |   1 | Song Jiang    |  25 | M      |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |   3 | Miejue Shitai |  25 | F      |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |   1 | Song Jiang    |  25 | M      |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |   3 | Miejue Shitai |  25 | F      |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |   1 | Song Jiang    |  25 | M      |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |   3 | Miejue Shitai |  25 | F      |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |   1 | Song Jiang    |  25 | M      |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |   3 | Miejue Shitai |  25 | F      |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |   1 | Song Jiang    |  25 | M      |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |   1 | Song Jiang    |  25 | M      |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |   1 | Song Jiang    |  25 | M      |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |   1 | Song Jiang    |  25 | M      |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |   1 | Song Jiang    |  25 | M      |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |   1 | Song Jiang    |  25 | M      |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |   1 | Song Jiang    |  25 | M      |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |   1 | Song Jiang    |  25 | M      |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |   1 | Song Jiang    |  25 | M      |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |   1 | Song Jiang    |  25 | M      |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |   1 | Song Jiang    |  25 | M      |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |   1 | Song Jiang    |  25 | M      |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |   1 | Song Jiang    |  25 | M      |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |   1 | Song Jiang    |  25 | M      |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |   1 | Song Jiang    |  25 | M      |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |   3 | Miejue Shitai |  25 | F      |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |   1 | Song Jiang    |  25 | M      |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |   3 | Miejue Shitai |  25 | F      |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |   1 | Song Jiang    |  25 | M      |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |   2 | Zhang Sanfeng |  25 | M      |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |   3 | Miejue Shitai |  25 | F      |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |   4 | Lin Chaoying  |  25 | F      |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |   1 | Song Jiang    |  25 | M      |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |      NULL |   1 | Song Jiang    |  25 | M      |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |      NULL |   1 | Song Jiang    |  25 | M      |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |      NULL |   1 | Song Jiang    |  25 | M      |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |      NULL |   3 | Miejue Shitai |  25 | F      |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    31 | Song Jiang    |  NULL |  18 | M      |      45 |      NULL |   1 | Song Jiang    |  25 | M      |
|    31 | Song Jiang    |  NULL |  18 | M      |      45 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    31 | Song Jiang    |  NULL |  18 | M      |      45 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    31 | Song Jiang    |  NULL |  18 | M      |      45 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    32 | Zhang Sanfeng |  NULL |  18 | M      |      94 |      NULL |   1 | Song Jiang    |  25 | M      |
|    32 | Zhang Sanfeng |  NULL |  18 | M      |      94 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    32 | Zhang Sanfeng |  NULL |  18 | M      |      94 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    32 | Zhang Sanfeng |  NULL |  18 | M      |      94 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |      NULL |   1 | Song Jiang    |  25 | M      |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |      NULL |   1 | Song Jiang    |  25 | M      |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |      NULL |   3 | Miejue Shitai |  25 | F      |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |      NULL |   4 | Lin Chaoying  |  25 | F      |
|    38 | abc           |  NULL |  20 | M      |    NULL |      NULL |   1 | Song Jiang    |  25 | M      |
|    38 | abc           |  NULL |  20 | M      |    NULL |      NULL |   2 | Zhang Sanfeng |  25 | M      |
|    38 | abc           |  NULL |  20 | M      |    NULL |      NULL |   3 | Miejue Shitai |  25 | F      |
|    38 | abc           |  NULL |  20 | M      |    NULL |      NULL |   4 | Lin Chaoying  |  25 | F      |
+-------+---------------+-------+-----+--------+---------+-----------+-----+---------------+-----+--------+
140 rows in set (0.00 sec)


第一张表   
                0  1  2  3
                1  2  3  4
第二张表   
                1  3  4  5
                2  3  4  5
交织衔接后结果：
                0 1 2 3   1 3 4 5
                0 1 2 3   2 3 4 5
                1 2 3 4   1 3 4 5
                1 2 3 4   2 3 4 5
两张表换下位置不影响数据只是显现结果变了罢了:
                1 3 4 5   0 1 2 3
                1 3 4 5   1 2 3 4
                2 3 4 5   0 1 2 3
                2 3 4 5   1 2 3 4

MariaDB [hellodb]> select * from teachers , s1;  （这个敕令也能够交织衔接然则比较老了引荐运用第一种）
+-----+---------------+-----+--------+-------+---------------+-------+-----+--------+---------+-----------+
| TID | Name          | Age | Gender | StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-----+---------------+-----+--------+-------+---------------+-------+-----+--------+---------+-----------+
|   1 | Song Jiang    |  25 | M      |     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|   2 | Zhang Sanfeng |  25 | M      |     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|   3 | Miejue Shitai |  25 | F      |     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|   4 | Lin Chaoying  |  25 | F      |     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|   1 | Song Jiang    |  25 | M      |     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|   2 | Zhang Sanfeng |  25 | M      |     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|   3 | Miejue Shitai |  25 | F      |     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|   4 | Lin Chaoying  |  25 | F      |     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|   1 | Song Jiang    |  25 | M      |     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|   2 | Zhang Sanfeng |  25 | M      |     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|   3 | Miejue Shitai |  25 | F      |     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|   4 | Lin Chaoying  |  25 | F      |     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |

挑出两张表的一般字段。

MariaDB [hellodb]> select name,age,gender from teachers cross join s1; (这里有两个字段是反复的name，age两个表都有)
ERROR 1052 (23000): Column 'name' in field list is ambiguous

MariaDB [hellodb]> select stuid,s1.name,tid,teachers.name from teachers cross join s1; （离别指定是哪一个表的name）
+-------+---------------+-----+---------------+
| stuid | name          | tid | name          |
+-------+---------------+-----+---------------+
|     1 | Shi Zhongyu   |   1 | Song Jiang    |
|     1 | Shi Zhongyu   |   2 | Zhang Sanfeng |
|     1 | Shi Zhongyu   |   3 | Miejue Shitai |
|     1 | Shi Zhongyu   |   4 | Lin Chaoying  |
|     2 | Shi Potian    |   1 | Song Jiang    |
|     2 | Shi Potian    |   2 | Zhang Sanfeng |
|     2 | Shi Potian    |   3 | Miejue Shitai |
|     2 | Shi Potian    |   4 | Lin Chaoying  |
|     3 | Xie Yanke     |   1 | Song Jiang    |
|     3 | Xie Yanke     |   2 | Zhang Sanfeng |
|     3 | Xie Yanke     |   3 | Miejue Shitai |
|     3 | Xie Yanke     |   4 | Lin Chaoying  |
|     4 | Ding Dian     |   1 | Song Jiang    |
|     4 | Ding Dian     |   2 | Zhang Sanfeng |
|     4 | Ding Dian     |   3 | Miejue Shitai |
|     4 | Ding Dian     |   4 | Lin Chaoying  |
|     5 | Yu Yutong     |   1 | Song Jiang    |
|     5 | Yu Yutong     |   2 | Zhang Sanfeng |
|     5 | Yu Yutong     |   3 | Miejue Shitai |
|     5 | Yu Yutong     |   4 | Lin Chaoying  |
|     6 | Shi Qing      |   1 | Song Jiang    |
|     6 | Shi Qing      |   2 | Zhang Sanfeng |
|     6 | Shi Qing      |   3 | Miejue Shitai |
|     6 | Shi Qing      |   4 | Lin Chaoying  |
|     7 | Xi Ren        |   1 | Song Jiang    |
|     7 | Xi Ren        |   2 | Zhang Sanfeng |
|     7 | Xi Ren        |   3 | Miejue Shitai |
|     7 | Xi Ren        |   4 | Lin Chaoying  |
|     8 | Lin Daiyu     |   1 | Song Jiang    |
|     8 | Lin Daiyu     |   2 | Zhang Sanfeng |
|     8 | Lin Daiyu     |   3 | Miejue Shitai |
|     8 | Lin Daiyu     |   4 | Lin Chaoying  |
|     9 | Ren Yingying  |   1 | Song Jiang    |
|     9 | Ren Yingying  |   2 | Zhang Sanfeng |
|     9 | Ren Yingying  |   3 | Miejue Shitai |
|     9 | Ren Yingying  |   4 | Lin Chaoying  |
|    10 | Yue Lingshan  |   1 | Song Jiang    |
|    10 | Yue Lingshan  |   2 | Zhang Sanfeng |
|    10 | Yue Lingshan  |   3 | Miejue Shitai |
|    10 | Yue Lingshan  |   4 | Lin Chaoying  |
|    11 | Yuan Chengzhi |   1 | Song Jiang    |
|    11 | Yuan Chengzhi |   2 | Zhang Sanfeng |
|    11 | Yuan Chengzhi |   3 | Miejue Shitai |
|    11 | Yuan Chengzhi |   4 | Lin Chaoying  |
                （省略了太长）

MariaDB [hellodb]> select stuid,s1.name,s1.age,tid,teachers.name,teachers.age from teachers cross join s1; （name和age都能够加在内里指定）
+-------+---------------+-----+-----+---------------+-----+
| stuid | name          | age | tid | name          | age |
+-------+---------------+-----+-----+---------------+-----+
|     1 | Shi Zhongyu   |  22 |   1 | Song Jiang    |  25 |
|     1 | Shi Zhongyu   |  22 |   2 | Zhang Sanfeng |  25 |
|     1 | Shi Zhongyu   |  22 |   3 | Miejue Shitai |  25 |
|     1 | Shi Zhongyu   |  22 |   4 | Lin Chaoying  |  25 |
|     2 | Shi Potian    |  22 |   1 | Song Jiang    |  25 |
|     2 | Shi Potian    |  22 |   2 | Zhang Sanfeng |  25 |
|     2 | Shi Potian    |  22 |   3 | Miejue Shitai |  25 |
|     2 | Shi Potian    |  22 |   4 | Lin Chaoying  |  25 |
|     3 | Xie Yanke     |  53 |   1 | Song Jiang    |  25 |
|     3 | Xie Yanke     |  53 |   2 | Zhang Sanfeng |  25 |
|     3 | Xie Yanke     |  53 |   3 | Miejue Shitai |  25 |
|     3 | Xie Yanke     |  53 |   4 | Lin Chaoying  |  25 |
|     4 | Ding Dian     |  32 |   1 | Song Jiang    |  25 |
|     4 | Ding Dian     |  32 |   2 | Zhang Sanfeng |  25 |
|     4 | Ding Dian     |  32 |   3 | Miejue Shitai |  25 |
|     4 | Ding Dian     |  32 |   4 | Lin Chaoying  |  25 |
|     5 | Yu Yutong     |  26 |   1 | Song Jiang    |  25 |
|     5 | Yu Yutong     |  26 |   2 | Zhang Sanfeng |  25 |
|     5 | Yu Yutong     |  26 |   3 | Miejue Shitai |  25 |
|     5 | Yu Yutong     |  26 |   4 | Lin Chaoying  |  25 |
                    （省略了太长）

MariaDB [hellodb]> select stuid,s1.name as s1_name,tid,teachers.name as teachers_name from teachers cross join s1;    (也能够加上别号来辨别比较清楚)
+-------+---------------+-----+---------------+
| stuid | s1_name       | tid | teachers_name |
+-------+---------------+-----+---------------+
|     1 | Shi Zhongyu   |   1 | Song Jiang    |
|     1 | Shi Zhongyu   |   2 | Zhang Sanfeng |
|     1 | Shi Zhongyu   |   3 | Miejue Shitai |
|     1 | Shi Zhongyu   |   4 | Lin Chaoying  |
|     2 | Shi Potian    |   1 | Song Jiang    |
|     2 | Shi Potian    |   2 | Zhang Sanfeng |
|     2 | Shi Potian    |   3 | Miejue Shitai |
|     2 | Shi Potian    |   4 | Lin Chaoying  |
|     3 | Xie Yanke     |   1 | Song Jiang    |
|     3 | Xie Yanke     |   2 | Zhang Sanfeng |
|     3 | Xie Yanke     |   3 | Miejue Shitai |
|     3 | Xie Yanke     |   4 | Lin Chaoying  |
                  （省略）

1. 对表起别号应用表的别号来查询数据。（定义别号是在字段的末了用在前面用，只在当前字段见效）

MariaDB [hellodb]> select stuid,s.name as s1_name,s.age,t.name as teachers_name,t.age from teachers t cross join s1 s;
+-------+---------------+-----+---------------+-----+
| stuid | s1_name       | age | teachers_name | age |
+-------+---------------+-----+---------------+-----+
|     1 | Shi Zhongyu   |  22 | Song Jiang    |  25 |
|     1 | Shi Zhongyu   |  22 | Zhang Sanfeng |  25 |
|     1 | Shi Zhongyu   |  22 | Miejue Shitai |  25 |
|     1 | Shi Zhongyu   |  22 | Lin Chaoying  |  25 |
|     2 | Shi Potian    |  22 | Song Jiang    |  25 |
|     2 | Shi Potian    |  22 | Zhang Sanfeng |  25 |
|     2 | Shi Potian    |  22 | Miejue Shitai |  25 |
|     2 | Shi Potian    |  22 | Lin Chaoying  |  25 |
|     3 | Xie Yanke     |  53 | Song Jiang    |  25 |
|     3 | Xie Yanke     |  53 | Zhang Sanfeng |  25 |
|     3 | Xie Yanke     |  53 | Miejue Shitai |  25 |
|     3 | Xie Yanke     |  53 | Lin Chaoying  |  25 |
|     4 | Ding Dian     |  32 | Song Jiang    |  25 |
|     4 | Ding Dian     |  32 | Zhang Sanfeng |  25 |
|     4 | Ding Dian     |  32 | Miejue Shitai |  25 |
|     4 | Ding Dian     |  32 | Lin Chaoying  |  25 |

MariaDB [hellodb]> select stuid,s1.name s1_name,s1.age,tid,t.name teacher_name,teachers.age from teachers t cross join s1;   （别号定义以后不能运用原始名字）
ERROR 1054 (42S22): Unknown column 'teachers.age' in 'field list'

内衔接

等值衔接：让表之间的字段以“等值”竖立衔接关联

把两个表有交集的处所衔接起来

MariaDB [hellodb]> select * from s1 inner join t1 on s1.teacherid=t1.tid;  （三个个先生各教一个门生）
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name        | Age | Gender | ClassID | TeacherID | TID | Name          | Age | Gender |
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
|     5 | Yu Yutong   |  26 | M      |       3 |         1 |   1 | Song Jiang    |  45 | M      |
|     1 | Shi Zhongyu |  22 | M      |       2 |         3 |   3 | Miejue Shitai |  77 | F      |
|     4 | Ding Dian   |  32 | M      |       4 |         4 |   4 | Lin Chaoying  |  93 | F      |
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
3 rows in set (0.00 sec)


MariaDB [hellodb]> update s1 set teacherid=1 where stuid=25;  （修正一下s1表的teacherid的值为1）
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [hellodb]> select * from s1 inner join t1 on s1.teacherid=t1.tid; （再次运用这条敕令，检察就是songjiang教两个门生）
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name        | Age | Gender | ClassID | TeacherID | TID | Name          | Age | Gender |
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
|     5 | Yu Yutong   |  26 | M      |       3 |         1 |   1 | Song Jiang    |  45 | M      |
|    25 | Sun Dasheng | 100 | M      |    NULL |         1 |   1 | Song Jiang    |  45 | M      |
|     1 | Shi Zhongyu |  22 | M      |       2 |         3 |   3 | Miejue Shitai |  77 | F      |
|     4 | Ding Dian   |  32 | M      |       4 |         4 |   4 | Lin Chaoying  |  93 | F      |
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

MariaDB [hellodb]> select * from s1 , t1 where s1.teacherid=t1.tid;  (不加 inner join 的老写法)
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name        | Age | Gender | ClassID | TeacherID | TID | Name          | Age | Gender |
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
|     5 | Yu Yutong   |  26 | M      |       3 |         1 |   1 | Song Jiang    |  45 | M      |
|    25 | Sun Dasheng | 100 | M      |    NULL |         1 |   1 | Song Jiang    |  45 | M      |
|     1 | Shi Zhongyu |  22 | M      |       2 |         3 |   3 | Miejue Shitai |  77 | F      |
|     4 | Ding Dian   |  32 | M      |       4 |         4 |   4 | Lin Chaoying  |  93 | F      |
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
4 rows in set (0.01 sec)

1. 内衔接以后过滤：先衔接再过滤，显现s1表大于30的人。

MariaDB [hellodb]> select * from s1 inner join t1 on s1.teacherid=t1.tid and s1.age >30;
+-------+-------------+-----+--------+---------+-----------+-----+--------------+-----+--------+
| StuID | Name        | Age | Gender | ClassID | TeacherID | TID | Name         | Age | Gender |
+-------+-------------+-----+--------+---------+-----------+-----+--------------+-----+--------+
|    25 | Sun Dasheng | 100 | M      |    NULL |         1 |   1 | Song Jiang   |  45 | M      |
|     4 | Ding Dian   |  32 | M      |       4 |         4 |   4 | Lin Chaoying |  93 | F      |
+-------+-------------+-----+--------+---------+-----------+-----+--------------+-----+--------+
2 rows in set (0.00 sec)

查询完以后过滤

MariaDB [hellodb]> select * from s1 inner join t1 on s1.teacherid=t1.tid where s1.a
+-------+-------------+-----+--------+---------+-----------+-----+--------------+--
| StuID | Name        | Age | Gender | ClassID | TeacherID | TID | Name         | A
+-------+-------------+-----+--------+---------+-----------+-----+--------------+--
|    25 | Sun Dasheng | 100 | M      |    NULL |         1 |   1 | Song Jiang   |  
|     4 | Ding Dian   |  32 | M      |       4 |         4 |   4 | Lin Chaoying |  
+-------+-------------+-----+--------+---------+-----------+-----+--------------+--
2 rows in set (0.00 sec)

外衔接

外衔接：
左外衔接：FROM tb1 LEFT JOIN tb2 ON tb1.col=tb2.col （排在前面的）
右外衔接：FROM tb1 RIGHT JOIN tb2 ON tb1.col=tb2.col （排在背面的）

左外衔接 left outer

门生表全留下来先生的只留下来有交集的处所。 (没有交集的处所空值替代)

MariaDB [hellodb]> select * from s1 left outer join t1 on s1.teacherid=t1.tid;  
+-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+
| StuID | Name          | Age | Gender | ClassID | TeacherID | TID  | Name          | Age  | Gender |
+-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+
|     1 | Shi Zhongyu   |  22 | M      |       2 |         3 |    3 | Miejue Shitai |   77 | F      |
|     2 | Shi Potian    |  22 | M      |       1 |         7 | NULL | NULL          | NULL | NULL   |
|     3 | Xie Yanke     |  53 | M      |       2 |        16 | NULL | NULL          | NULL | NULL   |
|     4 | Ding Dian     |  32 | M      |       4 |         4 |    4 | Lin Chaoying  |   93 | F      |
|     5 | Yu Yutong     |  26 | M      |       3 |         1 |    1 | Song Jiang    |   45 | M      |
|     6 | Shi Qing      |  46 | M      |       5 |      NULL | NULL | NULL          | NULL | NULL   |
|     7 | Xi Ren        |  19 | F      |       3 |      NULL | NULL | NULL          | NULL | NULL   |
|     8 | Lin Daiyu     |  17 | F      |       7 |      NULL | NULL | NULL          | NULL | NULL   |
|     9 | Ren Yingying  |  20 | F      |       6 |      NULL | NULL | NULL          | NULL | NULL   |
|    10 | Yue Lingshan  |  19 | F      |       3 |      NULL | NULL | NULL          | NULL | NULL   |
|    11 | Yuan Chengzhi |  23 | M      |       6 |      NULL | NULL | NULL          | NULL | NULL   |
|    12 | Wen Qingqing  |  19 | F      |       1 |      NULL | NULL | NULL          | NULL | NULL   |
|    13 | Tian Boguang  |  33 | M      |       2 |      NULL | NULL | NULL          | NULL | NULL   |
|    14 | Lu Wushuang   |  17 | F      |       3 |      NULL | NULL | NULL          | NULL | NULL   |
|    15 | Duan Yu       |  19 | M      |       4 |      NULL | NULL | NULL          | NULL | NULL   |
|    16 | Xu Zhu        |  21 | M      |       1 |      NULL | NULL | NULL          | NULL | NULL   |
|    17 | Lin Chong     |  25 | M      |       4 |      NULL | NULL | NULL          | NULL | NULL   |
|    18 | Hua Rong      |  23 | M      |       7 |      NULL | NULL | NULL          | NULL | NULL   |
|    19 | Xue Baochai   |  18 | F      |       6 |      NULL | NULL | NULL          | NULL | NULL   |
|    20 | Diao Chan     |  19 | F      |       7 |      NULL | NULL | NULL          | NULL | NULL   |
|    21 | Huang Yueying |  22 | F      |       6 |      NULL | NULL | NULL          | NULL | NULL   |
|    22 | Xiao Qiao     |  20 | F      |       1 |      NULL | NULL | NULL          | NULL | NULL   |
|    23 | Ma Chao       |  23 | M      |       4 |      NULL | NULL | NULL          | NULL | NULL   |
|    24 | Xu Xian       |  27 | M      |    NULL |      NULL | NULL | NULL          | NULL | NULL   |
|    25 | Sun Dasheng   | 100 | M      |    NULL |         1 |    1 | Song Jiang    |   45 | M      |
+-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+
25 rows in set (0.00 sec)

左外衔接扩大用法

• 掏出没有先生教的门生 (用where指定)

MariaDB [hellodb]> select * from t1;  （教师表）
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  93 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

MariaDB [hellodb]> select * from s1 left outer join t1 on s1.teacherid=t1.tid where tid is null; （前面两个，先生内外没有这两个先生的编号）
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
| StuID | Name          | Age | Gender | ClassID | TeacherID | TID  | Name | Age  | Gender |
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
|     2 | Shi Potian    |  22 | M      |       1 |         7 | NULL | NULL | NULL | NULL   |
|     3 | Xie Yanke     |  53 | M      |       2 |        16 | NULL | NULL | NULL | NULL   |
|     6 | Shi Qing      |  46 | M      |       5 |      NULL | NULL | NULL | NULL | NULL   |
|     7 | Xi Ren        |  19 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|     8 | Lin Daiyu     |  17 | F      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|     9 | Ren Yingying  |  20 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    10 | Yue Lingshan  |  19 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|    11 | Yuan Chengzhi |  23 | M      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    12 | Wen Qingqing  |  19 | F      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    13 | Tian Boguang  |  33 | M      |       2 |      NULL | NULL | NULL | NULL | NULL   |
|    14 | Lu Wushuang   |  17 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|    15 | Duan Yu       |  19 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    16 | Xu Zhu        |  21 | M      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    17 | Lin Chong     |  25 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    18 | Hua Rong      |  23 | M      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|    19 | Xue Baochai   |  18 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    20 | Diao Chan     |  19 | F      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|    21 | Huang Yueying |  22 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    22 | Xiao Qiao     |  20 | F      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    23 | Ma Chao       |  23 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    24 | Xu Xian       |  27 | M      |    NULL |      NULL | NULL | NULL | NULL | NULL   |
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
21 rows in set (0.00 sec)

右外链接：right outer

先生表全留下来，门生表有交集的处所留下来。

MariaDB [hellodb]> select * from s1 right outer join t1 on s1.teacherid=t1.tid;
+-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name        | Age  | Gender | ClassID | TeacherID | TID | Name          | Age | Gender |
+-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+
|     1 | Shi Zhongyu |   22 | M      |       2 |         3 |   3 | Miejue Shitai |  77 | F      |
|     4 | Ding Dian   |   32 | M      |       4 |         4 |   4 | Lin Chaoying  |  93 | F      |
|     5 | Yu Yutong   |   26 | M      |       3 |         1 |   1 | Song Jiang    |  45 | M      |
|    25 | Sun Dasheng |  100 | M      |    NULL |         1 |   1 | Song Jiang    |  45 | M      |
|  NULL | NULL        | NULL | NULL   |    NULL |      NULL |   2 | Zhang Sanfeng |  94 | M      |
+-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+
5 rows in set (0.00 sec)

右外衔接扩大用法

• 没有教门生的先生留下来。 (和左外衔接的逻辑是一样的)

MariaDB [hellodb]> select * from s1 right outer join t1 on s1.teacherid=t1.tid where s1.teacherid is null;
+-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name | Age  | Gender | ClassID | TeacherID | TID | Name          | Age | Gender |
+-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+
|  NULL | NULL | NULL | NULL   |    NULL |      NULL |   2 | Zhang Sanfeng |  94 | M      |
+-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+
1 row in set (0.00 sec)

完整外衔接

和交织衔接不一样     mysql不支持full outer join

把左外衔接和右外衔接用union团结起来，有交集的处所对应，没有交集的也处所输出出来。

MariaDB [hellodb]> select * from s1 left outer join t1 on s1.teacherid=t1.tid
    -> union
    -> select * from s1 right outer join t1 on s1.teacherid=t1.tid;
+-------+---------------+------+--------+---------+-----------+------+---------------+------+--------+
| StuID | Name          | Age  | Gender | ClassID | TeacherID | TID  | Name          | Age  | Gender |
+-------+---------------+------+--------+---------+-----------+------+---------------+------+--------+
|     1 | Shi Zhongyu   |   22 | M      |       2 |         3 |    3 | Miejue Shitai |   77 | F      |
|     2 | Shi Potian    |   22 | M      |       1 |         7 | NULL | NULL          | NULL | NULL   |
|     3 | Xie Yanke     |   53 | M      |       2 |        16 | NULL | NULL          | NULL | NULL   |
|     4 | Ding Dian     |   32 | M      |       4 |         4 |    4 | Lin Chaoying  |   93 | F      |
|     5 | Yu Yutong     |   26 | M      |       3 |         1 |    1 | Song Jiang    |   45 | M      |
|     6 | Shi Qing      |   46 | M      |       5 |      NULL | NULL | NULL          | NULL | NULL   |
|     7 | Xi Ren        |   19 | F      |       3 |      NULL | NULL | NULL          | NULL | NULL   |
|     8 | Lin Daiyu     |   17 | F      |       7 |      NULL | NULL | NULL          | NULL | NULL   |
|     9 | Ren Yingying  |   20 | F      |       6 |      NULL | NULL | NULL          | NULL | NULL   |
|    10 | Yue Lingshan  |   19 | F      |       3 |      NULL | NULL | NULL          | NULL | NULL   |
|    11 | Yuan Chengzhi |   23 | M      |       6 |      NULL | NULL | NULL          | NULL | NULL   |
|    12 | Wen Qingqing  |   19 | F      |       1 |      NULL | NULL | NULL          | NULL | NULL   |
|    13 | Tian Boguang  |   33 | M      |       2 |      NULL | NULL | NULL          | NULL | NULL   |
|    14 | Lu Wushuang   |   17 | F      |       3 |      NULL | NULL | NULL          | NULL | NULL   |
|    15 | Duan Yu       |   19 | M      |       4 |      NULL | NULL | NULL          | NULL | NULL   |
|    16 | Xu Zhu        |   21 | M      |       1 |      NULL | NULL | NULL          | NULL | NULL   |
|    17 | Lin Chong     |   25 | M      |       4 |      NULL | NULL | NULL          | NULL | NULL   |
|    18 | Hua Rong      |   23 | M      |       7 |      NULL | NULL | NULL          | NULL | NULL   |
|    19 | Xue Baochai   |   18 | F      |       6 |      NULL | NULL | NULL          | NULL | NULL   |
|    20 | Diao Chan     |   19 | F      |       7 |      NULL | NULL | NULL          | NULL | NULL   |
|    21 | Huang Yueying |   22 | F      |       6 |      NULL | NULL | NULL          | NULL | NULL   |
|    22 | Xiao Qiao     |   20 | F      |       1 |      NULL | NULL | NULL          | NULL | NULL   |
|    23 | Ma Chao       |   23 | M      |       4 |      NULL | NULL | NULL          | NULL | NULL   |
|    24 | Xu Xian       |   27 | M      |    NULL |      NULL | NULL | NULL          | NULL | NULL   |
|    25 | Sun Dasheng   |  100 | M      |    NULL |         1 |    1 | Song Jiang    |   45 | M      |
|  NULL | NULL          | NULL | NULL   |    NULL |      NULL |    2 | Zhang Sanfeng |   94 | M      |
+-------+---------------+------+--------+---------+-----------+------+---------------+------+--------+
26 rows in set (0.00 sec)

完整外衔接扩大用法：有交集的处所去撤除，只留外衔接。

• 把没有先生的门生，和没有门生的先生掏出来。

MariaDB [hellodb]> select * from (select s.stuid,s.name s_name,s.teacherid,t.tid,t.name t_name from s1 s left outer join t1  t on s.teacherid=t.tid union select s.stuid,s.name,s.teacherid,t.tid,t.name from s1 s right outer join t1 t on s.teacherid=t.tid) as a where a.teacherid is null or a.tid is null;
+-------+---------------+-----------+------+---------------+
| stuid | s_name        | teacherid | tid  | t_name        |
+-------+---------------+-----------+------+---------------+
|     2 | Shi Potian    |         7 | NULL | NULL          |
|     3 | Xie Yanke     |        16 | NULL | NULL          |
|     6 | Shi Qing      |      NULL | NULL | NULL          |
|     7 | Xi Ren        |      NULL | NULL | NULL          |
|     8 | Lin Daiyu     |      NULL | NULL | NULL          |
|     9 | Ren Yingying  |      NULL | NULL | NULL          |
|    10 | Yue Lingshan  |      NULL | NULL | NULL          |
|    11 | Yuan Chengzhi |      NULL | NULL | NULL          |
|    12 | Wen Qingqing  |      NULL | NULL | NULL          |
|    13 | Tian Boguang  |      NULL | NULL | NULL          |
|    14 | Lu Wushuang   |      NULL | NULL | NULL          |
|    15 | Duan Yu       |      NULL | NULL | NULL          |
|    16 | Xu Zhu        |      NULL | NULL | NULL          |
|    17 | Lin Chong     |      NULL | NULL | NULL          |
|    18 | Hua Rong      |      NULL | NULL | NULL          |
|    19 | Xue Baochai   |      NULL | NULL | NULL          |
|    20 | Diao Chan     |      NULL | NULL | NULL          |
|    21 | Huang Yueying |      NULL | NULL | NULL          |
|    22 | Xiao Qiao     |      NULL | NULL | NULL          |
|    23 | Ma Chao       |      NULL | NULL | NULL          |
|    24 | Xu Xian       |      NULL | NULL | NULL          |
|  NULL | NULL          |      NULL |    2 | Zhang Sanfeng |
+-------+---------------+-----------+------+---------------+
22 rows in set (0.00 sec)

三张表查询

取门生姓名，结果，科目。

先掏出门生的姓名和结果 （分两步做思路清楚一点）

MariaDB [hellodb]> select st.name,sc.courseid,sc.score from s1 st inner join scores sc on st.stuid=sc.stuid;
+-------------+----------+-------+
| name        | courseid | score |
+-------------+----------+-------+
| Shi Zhongyu |        2 |    77 |
| Shi Zhongyu |        6 |    93 |
| Shi Potian  |        2 |    47 |
| Shi Potian  |        5 |    97 |
| Xie Yanke   |        2 |    88 |
| Xie Yanke   |        6 |    75 |
| Ding Dian   |        5 |    71 |
| Ding Dian   |        2 |    89 |
| Yu Yutong   |        1 |    39 |
| Yu Yutong   |        7 |    63 |
| Shi Qing    |        1 |    96 |
| Xi Ren      |        1 |    86 |
| Xi Ren      |        7 |    83 |
| Lin Daiyu   |        4 |    57 |
| Lin Daiyu   |        3 |    93 |
+-------------+----------+-------+
15 rows in set (0.00 sec)

在衔接一次掏出门生姓名，结果，科目。

MariaDB [hellodb]> select st.name,co.course,sc.score from s1 st inner join scores sc on st.stuid=sc.stuid inner join courses co on sc.courseid=co.courseid;
+-------------+----------------+-------+
| name        | course         | score |
+-------------+----------------+-------+
| Shi Zhongyu | Kuihua Baodian |    77 |
| Shi Zhongyu | Weituo Zhang   |    93 |
| Shi Potian  | Kuihua Baodian |    47 |
| Shi Potian  | Daiyu Zanghua  |    97 |
| Xie Yanke   | Kuihua Baodian |    88 |
| Xie Yanke   | Weituo Zhang   |    75 |
| Ding Dian   | Daiyu Zanghua  |    71 |
| Ding Dian   | Kuihua Baodian |    89 |
| Yu Yutong   | Hamo Gong      |    39 |
| Yu Yutong   | Dagou Bangfa   |    63 |
| Shi Qing    | Hamo Gong      |    96 |
| Xi Ren      | Hamo Gong      |    86 |
| Xi Ren      | Dagou Bangfa   |    83 |
| Lin Daiyu   | Taiji Quan     |    57 |
| Lin Daiyu   | Jinshe Jianfa  |    93 |
+-------------+----------------+-------+
15 rows in set (0.00 sec)

严禁涌现四张表join的状况

自衔接

自联络望文生义就是把一张表假设为两张一样的表，然后在做“多表查询”

先构建一张表

MariaDB [hellodb]> create table emp (id int, name char(20),leaderid int);
Query OK, 0 rows affected (0.01 sec)

MariaDB [hellodb]> insert emp value(1,'huangshang',null);
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> insert emp value(2,'taihou','huangshang');
ERROR 1366 (22007): Incorrect integer value: 'huangshang' for column `hellodb`.`emp`.`leaderid` at row 1
MariaDB [hellodb]> insert emp value(2,'taihou',1);
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> insert emp value(3,'guifei',2);
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> insert emp value(4,'shufei',3);
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> select * from emp;
+------+------------+----------+
| id   | name       | leaderid |
+------+------------+----------+
|    1 | huangshang |     NULL |
|    2 | taihou     |        1 |
|    3 | guifei     |        2 |
|    4 | shufei     |        3 |
+------+------------+----------+
4 rows in set (0.00 sec)

查询内外的上级的姓名。

• 设想为两张表 员工表 和上司表 起别号做成

MariaDB [hellodb]> select * from emp as e inner join emp as l on e.leaderid=l.id;
+------+--------+----------+------+------------+----------+
| id   | name   | leaderid | id   | name       | leaderid |
+------+--------+----------+------+------------+----------+
|    2 | taihou |        1 |    1 | huangshang |     NULL |
|    3 | guifei |        2 |    2 | taihou     |        1 |
|    4 | shufei |        3 |    3 | guifei     |        2 |
+------+--------+----------+------+------------+----------+
3 rows in set (0.00 sec)

• 掏出来对应的上级，然则缺失了最上级。

MariaDB [hellodb]> select e.name emp,l.name leader from emp as e inner join emp as l on e.leaderid=l.id;
+--------+------------+
| emp    | leader     |
+--------+------------+
| taihou | huangshang |
| guifei | taihou     |
| shufei | guifei     |
+--------+------------+
3 rows in set (0.00 sec)

• 掏出每个人对应的上级的id。

MariaDB [hellodb]> select e.name emp,l.name leader from emp as e left join emp as l on e.leaderid=l.id;
+------------+------------+
| emp        | leader     |
+------------+------------+
| taihou     | huangshang |
| guifei     | taihou     |
| shufei     | guifei     |
| huangshang | NULL       |
+------------+------------+
4 rows in set (0.00 sec)

SQL语句的关键字实行递次

引荐进修：MySQL教程

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