MYSQL完全手册学习笔记（第十章）

连接

交叉连接



mysql> select * from color, attribute;
+-------+-----------+
| color | attribute |
+-------+-----------+
| black | eyes      |
| black | hair      |
| brown | eyes      |
| brown | hair      |
| gray  | eyes      |
| gray  | hair      |
+-------+-----------+
6 rows in set (0.00 sec)

这里面有个问题 当如果有4个表  每个包含100条记录的时候出来的结果会很多


内连接

mysql> select * from products;
+-----+------------+
| Pid | Pname      |
+-----+------------+
|   1 | apples     |
|   2 | oranges    |
|   3 | pineapples |
|   4 | bananas    |
+-----+------------+
4 rows in set (0.00 sec)

mysql> select * from sales;
+----+-----+----------+
| id | Pid | quantity |
+----+-----+----------+
|  1 | 3   | 2300     |
|  2 | 2   | 1500     |
|  3 | 1   | 3400     |
+----+-----+----------+
3 rows in set (0.00 sec)

mysql> select Pname ,quantity from products,sales where products.Pid=sales.Pid;
+------------+----------+
| Pname      | quantity |
+------------+----------+
| apples     | 3400     |
| oranges    | 1500     |
| pineapples | 2300     |
+------------+----------+
3 rows in set (0.05 sec)

mysql> select products,quantity from products,sales where products.Pid=sales.Pid
and sales.quantity>2000;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near 'sales
.quantity>2000' at line 1
mysql> select Pnama,quantity from products,sales where products.Pid=sales.Pidand
sales.quantity>2000;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near 'sales
.quantity>2000' at line 1
mysql> select Pname,quantity from products,sales where products.Pid=sales.Pidand
sales.quantity>2000;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near 'sales
.quantity>2000' at line 1
mysql> select Pname ,quantity from products,sales where products.Pid=sales.Pid;
+------------+----------+
| Pname      | quantity |
+------------+----------+
| apples     | 3400     |
| oranges    | 1500     |
| pineapples | 2300     |
+------------+----------+
3 rows in set (0.02 sec)

mysql> select Pname ,quantity from products,sales where products.Pid=sales.Pid a
nd sales.quantity>2000;
+------------+----------+
| Pname      | quantity |
+------------+----------+
| apples     | 3400     |
| pineapples | 2300     |
+------------+----------+
2 rows in set (0.02 sec)






mysql> select * from user;
+-----+-------+
| uid | name  |
+-----+-------+
| 100 | sue   |
| 103 | hary  |
| 104 | louis |
| 107 | sam   |
| 110 | james |
| 111 | mark  |
| 112 | rita  |
+-----+-------+
7 rows in set (0.00 sec)

mysql> select * from group;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near 'grou
' at line 1
mysql> select * from groups;
+-----+-----------+
| gid | name      |
+-----+-----------+
| 501 | authors   |
| 502 | actors    |
| 503 | musicians |
| 504 | chefs     |
+-----+-----------+
4 rows in set (0.00 sec)

mysql> select * from users_groups;
+-----+-----+
| uid | gid |
+-----+-----+
|  11 | 502 |
| 100 | 501 |
| 100 | 502 |
| 100 | 503 |
| 102 | 501 |
| 104 | 502 |
| 107 | 502 |
| 110 | 501 |
| 112 | 501 |
+-----+-----+
9 rows in set (0.00 sec)



mysql> select user.name,groups.name from user,groups,users_groups where user.uid
=users_groups.uid and groups.gid= users_groups.gid;
+-------+-----------+
| name  | name      |
+-------+-----------+
| sue   | authors   |
| james | authors   |
| rita  | authors   |
| sue   | actors    |
| louis | actors    |
| sam   | actors    |
| sue   | musicians |
+-------+-----------+
7 rows in set (0.01 sec)

左外连接
mysql> select * from user left join users_groups on user.uid=users_groups.uid;
从连接的左部（user表）选择所有的行，对于选中的每一行，或者从右部（users_groups表）显示相匹配的值（能够满足on或者using子句约束的值）。或者显示null的一行。这种类型的连接称为左外连接。

+-----+-------+------+------+
| uid | name  | uid  | gid  |
+-----+-------+------+------+
| 100 | sue   |  100 |  501 |
| 100 | sue   |  100 |  502 |
| 100 | sue   |  100 |  503 |
| 103 | hary  | NULL | NULL |
| 104 | louis |  104 |  502 |
| 107 | sam   |  107 |  502 |
| 110 | james |  110 |  501 |
| 111 | mark  | NULL | NULL |
| 112 | rita  |  112 |  501 |
+-----+-------+------+------+
9 rows in set (0.00 sec)


下面的语句和上面的结果是一样的


mysql> select * from user left join users_groups using(uid);
+-----+-------+------+
| uid | name  | gid  |
+-----+-------+------+
| 100 | sue   |  501 |
| 100 | sue   |  502 |
| 100 | sue   |  503 |
| 103 | hary  | NULL |
| 104 | louis |  502 |
| 107 | sam   |  502 |
| 110 | james |  501 |
| 111 | mark  | NULL |
| 112 | rita  |  501 |
+-----+-------+------+
9 rows in set (0.00 sec)

右外连接

mysql> select * from users_groups right join groups using(gid);
+-----+-----------+------+
| gid | name      | uid  |
+-----+-----------+------+
| 501 | authors   |  100 |
| 501 | authors   |  102 |
| 501 | authors   |  110 |
| 501 | authors   |  112 |
| 502 | actors    |   11 |
| 502 | actors    |  100 |
| 502 | actors    |  104 |
| 502 | actors    |  107 |
| 503 | musicians |  100 |
| 504 | chefs     | NULL |
+-----+-----------+------+
10 rows in set (0.00 sec)

通过浏览null 值，很容易看到哪一组没有成员
mysql> select * from users_groups right join groups using(gid) where uid is null
;
+-----+-------+------+
| gid | name  | uid  |
+-----+-------+------+
| 504 | chefs | NULL |
+-----+-------+------+
1 row in set (0.02 sec)





自查询

mysql> insert into menu(id,label,parent) values(1,'sevices','0');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(2,'company','0');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(3,'media center','0');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(4,'your account','0');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(5,'community','0');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(6,'for content publishers','1');

Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(7,'for small businesses','1');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(8,'backgroud','2');
Query OK, 1 row affected (0.05 sec)

mysql> insert into menu(id,label,parent) values(9,'client','2');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(10,'addresses','2');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(11,'jobs','2');
Query OK, 1 row affected (0.02 sec)

mysql> insert into menu(id,label,parent) values(11,'news','2');
ERROR 1062 (23000): Duplicate entry '11' for key 'PRIMARY'
mysql> insert into menu(id,label,parent) values(12,'news','2');
Query OK, 1 row affected (0.02 sec)

mysql> insert into menu(id,label,parent) values(13,'press releases','3');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(14,'media kit','3');
Query OK, 1 row affected (0.02 sec)

mysql> insert into menu(id,label,parent) values(15,'log in','4');
Query OK, 1 row affected (0.02 sec)

mysql> insert into menu(id,label,parent) values(16,'columns','5');
Query OK, 1 row affected (0.03 sec)

mysql> insert into menu(id,label,parent) values(17,'colophon','16');
Query OK, 1 row affected (0.02 sec)

mysql> insert into menu(id,label,parent) values(18,'cut','16');
Query OK, 1 row affected (0.02 sec)

mysql> insert into menu(id,label,parent) values(19,'boombox','16');
Query OK, 1 row affected (0.01 sec)

mysql> select * from menu;
+----+------------------------+--------+
| id | label                  | parent |
+----+------------------------+--------+
|  1 | sevices                | 0      |
|  2 | company                | 0      |
|  3 | media center           | 0      |
|  4 | your account           | 0      |
|  5 | community              | 0      |
|  6 | for content publishers | 1      |
|  7 | for small businesses   | 1      |
|  8 | backgroud              | 2      |
|  9 | client                 | 2      |
| 10 | addresses              | 2      |
| 11 | jobs                   | 2      |
| 12 | news                   | 2      |
| 13 | press releases         | 3      |
| 14 | media kit              | 3      |
| 15 | log in                 | 4      |
| 16 | columns                | 5      |
| 17 | colophon               | 16     |
| 18 | cut                    | 16     |
| 19 | boombox                | 16     |
+----+------------------------+--------+
19 rows in set (0.00 sec)








它创建了第一个表的虚拟拷贝，然后使用一个常规的内连接来把两个表映射到一起，并且得到需要的输出。



mysql> select a.label as parent_label,b.label as child_label from menu as a,menu
as b where a.id =b.id;
+------------------------+------------------------+
| parent_label           | child_label            |
+------------------------+------------------------+
| sevices                | sevices                |
| company                | company                |
| media center           | media center           |
| your account           | your account           |
| community              | community              |
| for content publishers | for content publishers |
| for small businesses   | for small businesses   |
| backgroud              | backgroud              |
| client                 | client                 |
| addresses              | addresses              |
| jobs                   | jobs                   |
| news                   | news                   |
| press releases         | press releases         |
| media kit              | media kit              |
| log in                 | log in                 |
| columns                | columns                |
| colophon               | colophon               |
| cut                    | cut                    |
| boombox                | boombox                |
+------------------------+------------------------+
19 rows in set (0.00 sec)


联合



mysql> select symbol,price from exchangea union select symbol,price from exchang
eb;
+--------+--------+
| symbol | price  |
+--------+--------+
| BGHU   | 12.90  |
| HDGS   | 6.48   |
| HDTE   | 123.71 |
| HTYF   | 90.10  |
| TDGB   | 78.44  |
| WERR   | 32.91  |
| YTEM   | 39.65  |
| DFRM   | 9.43   |
| HTYF   | 89.70  |
| POYT   | 87.10  |
| TDGB   | 79.00  |
+--------+--------+
11 rows in set (0.01 sec)




mysql> select symbol,price from exchangea where price >35.00 union select symbol
,price from exchangeb where price between 4.00 and 95.00;
+--------+--------+
| symbol | price  |
+--------+--------+
| HDTE   | 123.71 |
| HTYF   | 90.10  |
| TDGB   | 78.44  |
| YTEM   | 39.65  |
| DFRM   | 9.43   |
| HTYF   | 89.70  |
| POYT   | 87.10  |
| TDGB   | 79.00  |
+--------+--------+
8 rows in set (0.00 sec)


可以通过union运算符中添加all关键字来关掉mysql自动过滤重复记录的功能。


mysql> select symbol from exchangea union all select symbol from exchangeb;
+--------+
| symbol |
+--------+
| BGHU   |
| HDGS   |
| HDTE   |
| HTYF   |
| TDGB   |
| WERR   |
| YTEM   |
| DFRM   |
| HTYF   |
| POYT   |
| TDGB   |
+--------+
11 rows in set (0.00 sec)