多表查询:
建表
mysql> create table emp(emp_id int,emp_name char(10),emp_age tinyint, dpt_id int);
mysql> create table dpt(dpt_id int,dpt_name char(10));
insert into emp values(1,'robin',30,200);
insert into emp values(2,'zorro',25,200);
insert into emp values(3,'tom',22,200);
insert into emp values(4,'jerry',31,100);
insert into emp values(5,'jack',32,100);
insert into emp values(6,'rose',33,100);
insert into emp values(7,'king',40,300);
insert into emp values(8,'jean',41,300);
insert into emp values(9,'natasha',42,300);
insert into emp values(10,'xinghh',43,300);
insert into dpt values(100,'yw');
insert into dpt values(200,'kf');
insert into dpt values(300,'hr');
insert into dpt values(400,'boss');
alter table emp add emp_money int;
update emp set emp_money=10000 where emp_id=1;
update emp set emp_money=20000 where emp_id=2;
update emp set emp_money=30000 where emp_id=3;
update emp set emp_money=40000 where emp_id=4;
update emp set emp_money=50000 where emp_id=5;
update emp set emp_money=60000 where emp_id=6;
update emp set emp_money=70000 where emp_id=7;
update emp set emp_money=80000 where emp_id=8;
update emp set emp_money=90000 where emp_id=9;
update emp set emp_money=100000 where emp_id=10;mysql> select * from emp;
+--------+----------+---------+--------+-----------+
| emp_id | emp_name | emp_age | dpt_id | emp_money |
+--------+----------+---------+--------+-----------+
| 1 | robin | 30 | 200 | 10000 |
| 2 | zorro | 25 | 200 | 20000 |
| 3 | tom | 22 | 200 | 30000 |
| 4 | jerry | 31 | 100 | 40000 |
| 5 | jack | 32 | 100 | 50000 |
| 6 | rose | 33 | 100 | 60000 |
| 7 | king | 40 | 300 | 70000 |
| 8 | jean | 41 | 300 | 80000 |
| 9 | natasha | 42 | 300 | 90000 |
| 10 | xinghh | 43 | 300 | 100000 |
+--------+----------+---------+--------+-----------+
10 rows in set (0.00 sec)
mysql> select * from dpt;
+--------+----------+
| dpt_id | dpt_name |
+--------+----------+
| 100 | yw |
| 200 | kf |
| 300 | hr |
| 400 | boss |
+--------+----------+
4 rows in set (0.00 sec)
各种链接
等值链接(内连接) 只连接匹配的行
不等值连接
外连接－左连接 以左表为准
外连接－右连接 以右表为准
自连接
=================交叉连接======================= 迪卡尔集
mysql> select emp.emp_id,emp.emp_name,dpt.dpt_name from emp,dpt;
+--------+----------+----------+
| emp_id | emp_name | dpt_name |
+--------+----------+----------+
| 1 | robin | yw |
| 1 | robin | kf |
| 1 | robin | hr |
| 1 | robin | boss |
| 2 | zorro | yw |
| 2 | zorro | kf |
| 2 | zorro | hr |
| 2 | zorro | boss |
| 3 | tom | yw |
| 3 | tom | kf |
| 3 | tom | hr |
| 3 | tom | boss |
| 4 | jerry | yw |
| 4 | jerry | kf |
| 4 | jerry | hr |
| 4 | jerry | boss |
| 5 | jack | yw |
| 5 | jack | kf |
| 5 | jack | hr |
| 5 | jack | boss |
| 6 | rose | yw |
| 6 | rose | kf |
| 6 | rose | hr |
| 6 | rose | boss |
| 7 | king | yw |
| 7 | king | kf |
| 7 | king | hr |
| 7 | king | boss |
| 8 | jean | yw |
| 8 | jean | kf |
| 8 | jean | hr |
| 8 | jean | boss |
| 9 | natasha | yw |
| 9 | natasha | kf |
| 9 | natasha | hr |
| 9 | natasha | boss |
| 10 | xinghh | yw |
| 10 | xinghh | kf |
| 10 | xinghh | hr |
| 10 | xinghh | boss |
+--------+----------+----------+
40 rows in set (0.00 sec)
=================内连接======================= 等值连接
mysql> select emp.emp_id,emp.emp_name,dpt.dpt_name from emp,dpt where emp.dpt_id =dpt.dpt_id;
+--------+----------+----------+
| emp_id | emp_name | dpt_name |
+--------+----------+----------+
| 1 | robin | kf |
| 2 | zorro | kf |
| 3 | tom | kf |
| 4 | jerry | yw |
| 5 | jack | yw |
| 6 | rose | yw |
| 7 | king | hr |
| 8 | jean | hr |
| 9 | natasha | hr |
| 10 | xinghh | hr |
+--------+----------+----------+
10 rows in set (0.00 sec)
不等值连接
=================（左外连接 left join)=======================
mysql> select emp.emp_id,emp.emp_name,dpt.dpt_name from emp left join dpt on emp.dpt_id = dpt.dpt_id ;
+--------+----------+----------+
| emp_id | emp_name | dpt_name |
+--------+----------+----------+
| 4 | jerry | yw |
| 5 | jack | yw |
| 6 | rose | yw |
| 1 | robin | kf |
| 2 | zorro | kf |
| 3 | tom | kf |
| 7 | king | hr |
| 8 | jean | hr |
| 9 | natasha | hr |
| 10 | xinghh | hr |
+--------+----------+----------+
10 rows in set (0.00 sec)
=================（右外连接 right join)=======================
mysql> select emp.emp_id,emp.emp_name,dpt.dpt_name from emp left join dpt on emp.dpt_id = dpt.dpt_id order by emp_id;
+--------+----------+----------+
| emp_id | emp_name | dpt_name |
+--------+----------+----------+
| 1 | robin | kf |
| 2 | zorro | kf |
| 3 | tom | kf |
| 4 | jerry | yw |
| 5 | jack | yw |
| 6 | rose | yw |
| 7 | king | hr |
| 8 | jean | hr |
| 9 | natasha | hr |
| 10 | xinghh | hr |
+--------+----------+----------+
10 rows in set (0.00 sec)
子查询
mysql> select emp.emp_id,emp.emp_name,emp.emp_age,dpt.dpt_name from emp,dpt where emp.dpt_id = dpt.dpt_id and emp.emp_age > 25;
+--------+----------+---------+----------+
| emp_id | emp_name | emp_age | dpt_name |
+--------+----------+---------+----------+
| 4 | jerry | 31 | yw |
| 5 | jack | 32 | yw |
| 6 | rose | 33 | yw |
| 1 | robin | 30 | kf |
| 7 | king | 40 | hr |
| 8 | jean | 41 | hr |
| 9 | natasha | 42 | hr |
| 10 | xinghh | 43 | hr |
+--------+----------+---------+----------+
8 rows in set (0.00 sec)
mysql> select emp.emp_id,emp.emp_name,emp.emp_age,dpt.dpt_name from emp,dpt where emp.dpt_id = dpt.dpt_id order by emp.emp_age;
+--------+----------+---------+----------+
| emp_id | emp_name | emp_age | dpt_name |
+--------+----------+---------+----------+
| 3 | tom | 22 | kf |
| 2 | zorro | 25 | kf |
| 1 | robin | 30 | kf |
| 4 | jerry | 31 | yw |
| 5 | jack | 32 | yw |
| 6 | rose | 33 | yw |
| 7 | king | 40 | hr |
| 8 | jean | 41 | hr |
| 9 | natasha | 42 | hr |
| 10 | xinghh | 43 | hr |
+--------+----------+---------+----------+
10 rows in set (0.00 sec)
king hr:
1. ==========================
mysql> select emp_name from emp where emp_name='king';
+----------+
| emp_name |
+----------+
| king |
+----------+
1 row in set (0.00 sec)
自连接
求各部门最高的薪水
mysql> select max(emp_money) from emp group by dpt_id;
+----------------+
| max(emp_money) |
+----------------+
| 60000 |
| 30000 |
| 100000 |
+----------------+
3 rows in set (0.00 sec)
mysql> select * from emp;
+--------+----------+---------+--------+-----------+
| emp_id | emp_name | emp_age | dpt_id | emp_money |
+--------+----------+---------+--------+-----------+
| 1 | robin | 30 | 200 | 10000 |
| 2 | zorro | 25 | 200 | 20000 |
| 3 | tom | 22 | 200 | 30000 |
| 4 | jerry | 31 | 100 | 40000 |
| 5 | jack | 32 | 100 | 50000 |
| 6 | rose | 33 | 100 | 60000 |
| 7 | king | 40 | 300 | 70000 |
| 8 | jean | 41 | 300 | 80000 |
| 9 | natasha | 42 | 300 | 90000 |
| 10 | xinghh | 43 | 300 | 100000 |
+--------+----------+---------+--------+-----------+
10 rows in set (0.00 sec)
mysql> select emp_name,emp_money from emp,(select max(emp_money) as money from emp group by dpt_id) as new where emp_money=new.money;
+----------+-----------+
| emp_name | emp_money |
+----------+-----------+
| tom | 30000 |
| rose | 60000 |
| xinghh | 100000 |
+----------+-----------+
3 rows in set (0.01 sec)
mysql> create table new as(select emp_id as id,emp_name as name from emp);
Query OK, 10 rows affected (0.01 sec)
Records: 10 Duplicates: 0 Warnings: 0
mysql> show tables;
+----------------+
| Tables_in_mydb |
+----------------+
| dpt |
| emp |
| new |
| test |
| test1 |
| test2 |
| test3 |
| test4 |
| test5 |
| test6 |
+----------------+
10 rows in set (0.00 sec)
mysql> desc new;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | char(10) | YES | | NULL | |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> desc emp;
+-----------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+------------+------+-----+---------+-------+
| emp_id | int(11) | YES | | NULL | |
| emp_name | char(10) | YES | | NULL | |
| emp_age | tinyint(4) | YES | | NULL | |
| dpt_id | int(11) | YES | | NULL | |
| emp_money | int(11) | YES | | NULL | |
+-----------+------------+------+-----+---------+-------+
5 rows in set (0.01 sec)
mysql> select * from new;
+------+---------+
| id | name |
+------+---------+
| 1 | robin |
| 2 | zorro |
| 3 | tom |
| 4 | jerry |
| 5 | jack |
| 6 | rose |
| 7 | king |
| 8 | jean |
| 9 | natasha |
| 10 | xinghh |
+------+---------+
10 rows in set (0.00 sec)
船舰一个结构一样但是没有数据的表
mysql> create table new2 as (select * from emp where 1=2);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show tables;
+----------------+
| Tables_in_mydb |
+----------------+
| dpt |
| emp |
| new |
| new2 |
| test |
| test1 |
| test2 |
| test3 |
| test4 |
| test5 |
| test6 |
+----------------+
11 rows in set (0.00 sec)
mysql> desc new2
-> ;
+-----------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+------------+------+-----+---------+-------+
| emp_id | int(11) | YES | | NULL | |
| emp_name | char(10) | YES | | NULL | |
| emp_age | tinyint(4) | YES | | NULL | |
| dpt_id | int(11) | YES | | NULL | |
| emp_money | int(11) | YES | | NULL | |
+-----------+------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
mysql> select * from new2
-> ;
Empty set (0.00 sec)