操作表的SQL语句补充 、表查询关键字、多表查询
操作表的SQL语句补充
1.修改表名
alter table 旧表名 rename 新表名;
mysql> create table t1(id int primary key auto_increment,name varchar(32));
Query OK, 0 rows affected (0.03 sec)
mysql> alter table t1 rename t2;
Query OK, 0 rows affected (0.02 sec)
mysql> show tables;
+--------------+
| Tables_in_d6 |
+--------------+
| t2 |
+--------------+
2.新增字段
1.alter table 表名 add 字段名 字段类型(数字) 约束条件;
mysql> desc t2;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(32) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.05 sec)
mysql> alter table t2 add gender varchar(32) default 'male';
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t2;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(32) | YES | | NULL | |
| gender | varchar(32) | YES | | male | |
+--------+-------------+------+-----+---------+----------------+
- 指定字段添加到某个字段后：alter table 表名 add 字段名 字段类型(数字) 约束条件 after 已经存在的字段；
mysql> alter table t2 add age int after name;
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t2;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| gender | varchar(32) | YES | | male | |
+--------+-------------+------+-----+---------+----------------+
- 指定字段添加到表的第一排：alter table 表名 add 字段名 字段类型(数字) 约束条件 first;
mysql> alter table t2 add vid int first;
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t2;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| vid | int(11) | YES | | NULL | |
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| gender | varchar(32) | YES | | male | |
+--------+-------------+------+-----+---------+----------------+
修改字段
1.alter table 表名 change 旧字段 新字段 字段类型(字段名) 约束条件
mysql> alter table t2 change vid class varchar(32);
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t2;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| class | varchar(32) | YES | | NULL | |
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| gender | varchar(32) | YES | | male | |
+--------+-------------+------+-----+---------+----------------+
- 只修改字段名的字段类型(约束条件) : alter table 表名 modify 字段名 新的字段类型(数字) 约束条件
mysql> alter table t2 modify class varchar(16);
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t2;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| class | varchar(16) | YES | | NULL | |
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| gender | varchar(32) | YES | | male | |
+--------+-------------+------+-----+---------+----------------+
删除字段
alter table 表名 drop 字段名
mysql> alter table t2 drop class;
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t2;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| gender | varchar(32) | YES | | male | |
+--------+-------------+------+-----+---------+----------------+
表查询关键字
数据准备
create table emp(
id int not null unique auto_increment,
name varchar(20) not null,
sex enum('male','female') not null default 'male', #大部分是男的
age int(3) unsigned not null default 28,
hire_date date not null,
post varchar(50),
post_comment varchar(100),
salary double(15,2),
office int, #一个部门一个屋子
depart_id int
);
#三个部门：教学，销售，运营
insert into emp(name,sex,age,hire_date,post,salary,office,depart_id) values
('jason','male',18,'20170301','浦东第一帅形象代言',7300.33,401,1), #以下是教学部
('tom','male',78,'20150302','teacher',1000000.31,401,1),
('kevin','male',81,'20130305','teacher',8300,401,1),
('tony','male',73,'20140701','teacher',3500,401,1),
('owen','male',28,'20121101','teacher',2100,401,1),
('jack','female',18,'20110211','teacher',9000,401,1),
('jenny','male',18,'19000301','teacher',30000,401,1),
('sank','male',48,'20101111','teacher',10000,401,1),
('哈哈','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门
('呵呵','female',38,'20101101','sale',2000.35,402,2),
('西西','female',18,'20110312','sale',1000.37,402,2),
('乐乐','female',18,'20160513','sale',3000.29,402,2),
('拉拉','female',28,'20170127','sale',4000.33,402,2),
('僧龙','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门
('程咬金','male',18,'19970312','operation',20000,403,3),
('程咬银','female',18,'20130311','operation',19000,403,3),
('程咬铜','male',18,'20150411','operation',18000,403,3),
('程咬铁','female',18,'20140512','operation',17000,403,3);
查询关键字之select与from
select 后接需要查询表中数据对应的字段名或全部字段名(*)；from 后接指定的操作的对象(可以是一张表，也可以是多张表)；select ....from ...指从某张表中获取某个字段名(全部字段名)的数据
1.SQL语句的关键字编写的顺序与执行顺序是不一致的
eg: select name from t1;
执行顺序：先执行from t1 确定表名，再执行select name 查找name字段
2.我们在编写SQL语句针对select和from可以先写一个固定模板：select * from 表名 其他操作，因为select后的字段可能是实际的，也可能是同过SQL动态产生的，所以先用*站位，最后在修改
查询关键字之where
1.查询id大于等于3小于等于6的数据
select * from emp where id >=3 and id <=6;
mysql> select * from emp where id >=3 and id <=6;
+----+-------+--------+-----+------------+---------+--------------+---------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-------+--------+-----+------------+---------+--------------+---------+--------+-----------+
| 3 | kevin | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 5 | owen | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 6 | jack | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
+----+-------+--------+-----+------------+---------+--------------+---------+--------+-----------+
select * from emp where id between 3 and 6;
mysql> select * from emp where id between 3 and 6;
+----+-------+--------+-----+------------+---------+--------------+---------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-------+--------+-----+------------+---------+--------------+---------+--------+-----------+
| 3 | kevin | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 5 | owen | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 6 | jack | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
+----+-------+--------+-----+------------+---------+--------------+---------+--------+-----------+
2.查询薪资是20000或者18000或者17000的数据
select * from emp where salary = 20000 or salary =18000 or salary =17000;
mysql> select * from emp where salary = 20000 or salary =18000 or salary =17000;
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
成员运算：select * from emp where salary in (20000,18000,17000);
mysql> select * from emp where salary in (20000,18000,17000);
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
3.查询员工姓名中包含o字母的员工姓名和薪资
select * from emp where name like '%o%';
mysql> select * from emp where name like '%o%';
+----+-------+------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-------+------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 5 | owen | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
+----+-------+------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
4.查询员工姓名是由四个字符组成的员工姓名与其薪资
select name,salary from emp where char_length(name) = 4;
mysql> select name,salary from emp where char_length(name) = 4;
+------+----------+
| name | salary |
+------+----------+
| tony | 3500.00 |
| owen | 2100.00 |
| jack | 9000.00 |
| sank | 10000.00 |
+------+----------+
select name,salary from emp where name like '____';
mysql> select name,salary from emp where name like '____';
+------+----------+
| name | salary |
+------+----------+
| tony | 3500.00 |
| owen | 2100.00 |
| jack | 9000.00 |
| sank | 10000.00 |
+------+----------+
5.查询id小于3或者大于6的数据
select * from emp where id ❤️ or id >6;
mysql> select * from emp where id <3 or id >6;
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 7 | jenny | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 8 | sank | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 9 | 哈哈 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 10 | 呵呵 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 11 | 西西 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 12 | 乐乐 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 13 | 拉拉 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 14 | 僧龙 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
select * from emp where id not between 3 and 6;
mysql> select * from emp where id not between 3 and 6;
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 7 | jenny | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 8 | sank | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 9 | 哈哈 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 10 | 呵呵 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 11 | 西西 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 12 | 乐乐 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 13 | 拉拉 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 14 | 僧龙 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
6.查询薪资不在20000，18000，17000范围的数据
select * from emp where salary not in (20000,18000,17000);
mysql> select * from emp where salary not in (20000,18000,17000);
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 3 | kevin | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 5 | owen | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 6 | jack | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 7 | jenny | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 8 | sank | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 9 | 哈哈 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 10 | 呵呵 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 11 | 西西 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 12 | 乐乐 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 13 | 拉拉 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 14 | 僧龙 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
7.查询岗位描述为空的员工名与岗位名
select name,post from emp where post_comment is null;
mysql> select name,post from emp where post_comment is null;
+-----------+-----------------------------+
| name | post |
+-----------+-----------------------------+
| jason | 浦东第一帅形象代言 |
| tom | teacher |
| kevin | teacher |
| tony | teacher |
| owen | teacher |
| jack | teacher |
| jenny | teacher |
| sank | teacher |
| 哈哈 | sale |
| 呵呵 | sale |
| 西西 | sale |
| 乐乐 | sale |
| 拉拉 | sale |
| 僧龙 | operation |
| 程咬金 | operation |
| 程咬银 | operation |
| 程咬铜 | operation |
| 程咬铁 | operation |
+-----------+-----------------------------+
查询关键字之group by 分组
分组：按照一些指定的条件将单个单个的数据分为一个个的整体
mysql> select * from emp group by post;
+----+--------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+--------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 14 | 僧龙 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 9 | 哈哈 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
+----+--------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
ps:
1.问题：分组之后我们研究的对象应该是以组为单位，不应该在直接获取单个数据项，如果获取了应该直接报错，select后面可以直接填写的字段名只能是分组的依据(其他字段需要借助于一些方法才可以获取)
2.解决添加：set global sql_mode='strict_trans_tables,only_full_group_by';
MySQL最常用分组聚合函数
配合分组常见使用的聚合函数：max、min、sum、count、avg、group_concat(不仅可以用来显示除分组以外字段数据还可拼接字符串的作用,ps:分组之后使用)
ps:我们写SQL是否需要使用分组，可以在题目中得到答案，比如：每个、平均、最大、最小
练习
1.获取每个部门的最高工资
select post as '部门',max(salary) as '最高工资' from emp group by post;
mysql> select post as '部门',max(salary) as '最高工资' from emp group by post;
+-----------------------------+--------------+
| 部门 | 最高工资 |
+-----------------------------+--------------+
| operation | 20000.00 |
| sale | 4000.33 |
| teacher | 1000000.31 |
| 浦东第一帅形象代言 | 7300.33 |
+-----------------------------+--------------+
2.每个部门的最低工资
select post as '部门',min(salary) as '最低工资' from emp group by post;
mysql> select post as '部门',min(salary) as '最低工资' from emp group by post;
+-----------------------------+--------------+
| 部门 | 最低工资 |
+-----------------------------+--------------+
| operation | 10000.13 |
| sale | 1000.37 |
| teacher | 2100.00 |
| 浦东第一帅形象代言 | 7300.33 |
+-----------------------------+--------------+
3.每个部门的平均工资
select post,avg(salary) from emp group by post;
mysql> select post,avg(salary) from emp group by post;
+-----------------------------+---------------+
| post | avg(salary) |
+-----------------------------+---------------+
| operation | 16800.026000 |
| sale | 2600.294000 |
| teacher | 151842.901429 |
| 浦东第一帅形象代言 | 7300.330000 |
+-----------------------------+---------------+
4.每个部门的工资总和
select post,sum(salary) from emp group by post;
mysql> select post,sum(salary) from emp group by post;
+-----------------------------+-------------+
| post | sum(salary) |
+-----------------------------+-------------+
| operation | 84000.13 |
| sale | 13001.47 |
| teacher | 1062900.31 |
| 浦东第一帅形象代言 | 7300.33 |
+-----------------------------+-------------+
5.每个部门的人数
select post,count(id) from emp group by post;
mysql> select post,count(id) from emp group by post;
+-----------------------------+-----------+
| post | count(id) |
+-----------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 浦东第一帅形象代言 | 1 |
+-----------------------------+-----------+
6.查询分组之后的部门名称和每个部门下所有的学生姓名
select post,group_concat(name) from emp group by post;
mysql> select post,group_concat(name) from emp group by post;
+-----------------------------+------------------------------------------------+
| post | group_concat(name) |
+-----------------------------+------------------------------------------------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,僧龙 |
| sale | 拉拉,乐乐,西西,呵呵,哈哈 |
| teacher | sank,jenny,jack,owen,tony,kevin,tom |
| 浦东第一帅形象代言 | jason |
+-----------------------------+------------------------------------------------+
7.查询分组之后的部门名称和每个部门下所有的学生姓名及对应工资(name:salary)
mysql> select post,group_concat(name,':',salary) from emp group by post;
+-----------------------------+--------------------------------------------------------------------------------------------------+
| post | group_concat(name,':',salary) |
+-----------------------------+--------------------------------------------------------------------------------------------------+
| operation | 程咬铁:17000.00,程咬铜:18000.00,程咬银:19000.00,程咬金:20000.00,僧龙:10000.13 |
| sale | 拉拉:4000.33,乐乐:3000.29,西西:1000.37,呵呵:2000.35,哈哈:3000.13 |
| teacher | sank:10000.00,jenny:30000.00,jack:9000.00,owen:2100.00,tony:3500.00,kevin:8300.00,tom:1000000.31 |
| 浦东第一帅形象代言 | jason:7300.33 |
+-----------------------------+--------------------------------------------------------------------------------------------------+
查询关键字之having过滤
where 与 having 的功能其实是一样的，都是用来筛选数据，只不过where用于分组之前筛选，而having用于分组之后筛选，为了人为区分，所以将where叫筛选，having叫过滤
1、统计各部门年龄在30岁以上的员工平均工资，并且保留平均工资大于10000的部门
select post,avg(salary) from emp where age >=30 group by post having avg(salary)>10000;
mysql> select * from emp where age >=30;
+----+--------+--------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+--------+--------+-----+------------+---------+--------------+------------+--------+-----------+
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 3 | kevin | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 8 | sank | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 9 | 哈哈 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 10 | 呵呵 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
+----+--------+--------+-----+------------+---------+--------------+------------+--------+-----------+
6 rows in set (0.00 sec)
mysql> select post,avg(salary) from emp where age >=30 group by post;
+---------+---------------+
| post | avg(salary) |
+---------+---------------+
| sale | 2500.240000 |
| teacher | 255450.077500 |
+---------+---------------+
2 rows in set (0.00 sec)
mysql> select post,avg(salary) from emp where age >=30 group by post having avg(salary)>10000;
+---------+---------------+
| post | avg(salary) |
+---------+---------------+
| teacher | 255450.077500 |
+---------+---------------+
1 row in set (0.00 sec)
查询关键字之distinct去重
去重:去除重复的，前提是数据必须是一模一样
1.去除年龄重复的数据
select distinct age from emp;
mysql> select distinct age from emp;
+-----+
| age |
+-----+
| 18 |
| 78 |
| 81 |
| 73 |
| 28 |
| 48 |
| 38 |
+-----+
查询关键字之order by 排序
在order by排序中，默认是升序(asc),如果想要降序，只需在最后加上desc
1.按照工资升序
select * from emp order by salary;
mysql> select * from emp order by salary;
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 11 | 西西 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 10 | 呵呵 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 5 | owen | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 9 | 哈哈 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 12 | 乐乐 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 13 | 拉拉 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 3 | kevin | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 6 | jack | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 8 | sank | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 14 | 僧龙 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 7 | jenny | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
2.按照工资降序
select * from emp order by salary desc;
mysql> select * from emp order by salary desc;
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 7 | jenny | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
| 14 | 僧龙 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 8 | sank | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 6 | jack | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 3 | kevin | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 13 | 拉拉 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 12 | 乐乐 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 9 | 哈哈 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 5 | owen | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 10 | 呵呵 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 11 | 西西 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
3.先按照age降序排，在年龄相同的情况下再按照薪资升序排
select * from emp order by age desc,salary asc;
mysql> select * from emp order by age desc,salary asc;
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 3 | kevin | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 9 | 哈哈 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 8 | sank | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 10 | 呵呵 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 5 | owen | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 13 | 拉拉 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 14 | 僧龙 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 11 | 西西 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 12 | 乐乐 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 6 | jack | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 7 | jenny | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
4.统计各部门年龄在10岁以上的员工平均工资，并且保留平均工资大于1000的部门，然后对平均工资进行排序
select post,avg(salary) from emp where age >10 group by post having avg(salary)>1000 order by avg(salary);
mysql> select post,avg(salary) from emp where age >10 group by post;
+-----------------------------+---------------+
| post | avg(salary) |
+-----------------------------+---------------+
| operation | 16800.026000 |
| sale | 2600.294000 |
| teacher | 151842.901429 |
| 浦东第一帅形象代言 | 7300.330000 |
+-----------------------------+---------------+
4 rows in set (0.00 sec)
mysql> select post,avg(salary) from emp where age >10 group by post having avg(salary)>1000;
+-----------------------------+---------------+
| post | avg(salary) |
+-----------------------------+---------------+
| operation | 16800.026000 |
| sale | 2600.294000 |
| teacher | 151842.901429 |
| 浦东第一帅形象代言 | 7300.330000 |
+-----------------------------+---------------+
4 rows in set (0.00 sec)
mysql> select post,avg(salary) from emp where age >10 group by post having avg(salary)>1000 order by avg(salary);
+-----------------------------+---------------+
| post | avg(salary) |
+-----------------------------+---------------+
| sale | 2600.294000 |
| 浦东第一帅形象代言 | 7300.330000 |
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------------------------+---------------+
查询关键字之limit分页
limit 分页：可以限制数据展示的条数，节省内存
limit n:表示展示前n t条数据；limit n,m 第一个参数n表示从第n个数据开始，第二个参数m表示展示m条数据
1.查询工资最高的人的详细信息
select * from emp order by salary desc limit 1;
mysql> select * from emp order by salary desc;
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 7 | jenny | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
| 14 | 僧龙 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 8 | sank | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 6 | jack | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 3 | kevin | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 13 | 拉拉 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 12 | 乐乐 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 9 | 哈哈 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 5 | owen | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 10 | 呵呵 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 11 | 西西 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
18 rows in set (0.00 sec)
mysql> select * from emp order by salary desc limit 1;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| 2 | tom | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
2.查询工资排序(升序)之后第5条数据之后的6个人详细信息
select * from emp order by salary limit 5,6;
mysql> select * from emp order by salary limit 5,6;
+----+--------+--------+-----+------------+-----------------------------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+--------+--------+-----+------------+-----------------------------+--------------+----------+--------+-----------+
| 4 | tony | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 13 | 拉拉 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 3 | kevin | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 6 | jack | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 8 | sank | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
+----+--------+--------+-----+------------+-----------------------------+--------------+----------+--------+-----------+
查询关键字之regexp正则
正则表达式本质上是使用一些符号的组合产生一些特殊的含义，然后去字符串中筛选出符合条件的数据
筛选出名字以j开头，以n或者y结尾的详细数据
select * from emp where name regexp '^j.*(n|y)$';
mysql> select * from emp where name regexp '^j.*(n|y)$';
+----+-------+------+-----+------------+-----------------------------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-------+------+-----+------------+-----------------------------+--------------+----------+--------+-----------+
| 1 | jason | male | 18 | 2017-03-01 | 浦东第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 7 | jenny | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
+----+-------+------+-----+------------+-----------------------------+--------------+----------+--------+-----------+
多表查询
多表查询有两种方式：子查询、连表操作
数据准备
#建表
create table dep1(
id int primary key auto_increment,
name varchar(20)
);
create table emp1(
id int primary key auto_increment,
name varchar(20),
gender enum('male','female') not null default 'male',
age int,
dep_id int
);
#插入数据
insert into dep1 values
(200,'技术'),
(201,'人力资源'),
(202,'销售'),
(203,'运营'),
(205,'安保')
;
insert into emp1(name,gender,age,dep_id) values
('jason','male',18,200),
('dragon','female',48,201),
('kevin','male',18,201),
('nick','male',28,202),
('owen','male',18,203),
('jerry','female',18,204);
子查询
子查询就是将一张表的查询结果括号括起来当做另外一条SQL语句的条件
类似于日常生活解决问题的方式：第一步干什么，第二步基于第一步的结果在做什么操作
查询jason的部门名称
select dep_id from emp1 where name = 'jason'; 得到结果部门编号为200
select * from dep1 where id = 200;
mysql> select dep_id from emp1 where name = 'jason';
+--------+
| dep_id |
+--------+
| 200 |
+--------+
1 row in set (0.00 sec)
mysql> select * from dep1 where id = 200;
+-----+--------+
| id | name |
+-----+--------+
| 200 | 技术 |
+-----+--------+
1 row in set (0.00 sec)
select * from dep1 where id = (select dep_id from emp1 where name = 'jason');
mysql> select * from dep1 where id = (select dep_id from emp1 where name = 'jason');
+-----+--------+
| id | name |
+-----+--------+
| 200 | 技术 |
+-----+--------+
1 row in set (0.00 sec)
连表操作
连表操作就是先将所有涉及到结果的表全部拼接到一起形成一张大表，然后从大表中查询数据
如果直接用select * from 表1，表2 将两张表直接拼接，会出现笛卡尔积情况；我们不会使用笛卡尔积来求数据，因为效率太低，并且连表有专门的语法
mysql> select * from emp1,dep1;
+----+--------+--------+------+--------+-----+--------------+
| id | name | gender | age | dep_id | id | name |
+----+--------+--------+------+--------+-----+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 1 | jason | male | 18 | 200 | 201 | 人力资源 |
| 1 | jason | male | 18 | 200 | 202 | 销售 |
| 1 | jason | male | 18 | 200 | 203 | 运营 |
| 1 | jason | male | 18 | 200 | 205 | 安保 |
| 2 | dragon | female | 48 | 201 | 200 | 技术 |
| 2 | dragon | female | 48 | 201 | 201 | 人力资源 |
| 2 | dragon | female | 48 | 201 | 202 | 销售 |
| 2 | dragon | female | 48 | 201 | 203 | 运营 |
| 2 | dragon | female | 48 | 201 | 205 | 安保 |
| 3 | kevin | male | 18 | 201 | 200 | 技术 |
| 3 | kevin | male | 18 | 201 | 201 | 人力资源 |
| 3 | kevin | male | 18 | 201 | 202 | 销售 |
| 3 | kevin | male | 18 | 201 | 203 | 运营 |
| 3 | kevin | male | 18 | 201 | 205 | 安保 |
| 4 | nick | male | 28 | 202 | 200 | 技术 |
| 4 | nick | male | 28 | 202 | 201 | 人力资源 |
| 4 | nick | male | 28 | 202 | 202 | 销售 |
| 4 | nick | male | 28 | 202 | 203 | 运营 |
| 4 | nick | male | 28 | 202 | 205 | 安保 |
| 5 | owen | male | 18 | 203 | 200 | 技术 |
| 5 | owen | male | 18 | 203 | 201 | 人力资源 |
| 5 | owen | male | 18 | 203 | 202 | 销售 |
| 5 | owen | male | 18 | 203 | 203 | 运营 |
| 5 | owen | male | 18 | 203 | 205 | 安保 |
| 6 | jerry | female | 18 | 204 | 200 | 技术 |
| 6 | jerry | female | 18 | 204 | 201 | 人力资源 |
| 6 | jerry | female | 18 | 204 | 202 | 销售 |
| 6 | jerry | female | 18 | 204 | 203 | 运营 |
| 6 | jerry | female | 18 | 204 | 205 | 安保 |
+----+--------+--------+------+--------+-----+--------------+
mysql> select * from emp1,dep1 where emp1.dep_id = dep1.id;
+----+--------+--------+------+--------+-----+--------------+
| id | name | gender | age | dep_id | id | name |
+----+--------+--------+------+--------+-----+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | dragon | female | 48 | 201 | 201 | 人力资源 |
| 3 | kevin | male | 18 | 201 | 201 | 人力资源 |
| 4 | nick | male | 28 | 202 | 202 | 销售 |
| 5 | owen | male | 18 | 203 | 203 | 运营 |
+----+--------+--------+------+--------+-----+--------------+
mysql> select emp1.name,dep1.name from emp1,dep1 where emp1.dep_id = dep1.id;
+--------+--------------+
| name | name |
+--------+--------------+
| jason | 技术 |
| dragon | 人力资源 |
| kevin | 人力资源 |
| nick | 销售 |
| owen | 运营 |
+--------+--------------+
连表操作的语法
1.inner join
inner join 是内连接，只拼接两边都有的字段数据 (表1 inner join 表2 on 连接条件)
mysql> select * from emp1 inner join dep1 on emp1.dep_id = dep1.id;
+----+--------+--------+------+--------+-----+--------------+
| id | name | gender | age | dep_id | id | name |
+----+--------+--------+------+--------+-----+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | dragon | female | 48 | 201 | 201 | 人力资源 |
| 3 | kevin | male | 18 | 201 | 201 | 人力资源 |
| 4 | nick | male | 28 | 202 | 202 | 销售 |
| 5 | owen | male | 18 | 203 | 203 | 运营 |
+----+--------+--------+------+--------+-----+--------------+
5 rows in set (0.00 sec)
mysql> select emp1.name,dep1.name from emp1 inner join dep1 on emp1.dep_id = dep1.id;
+--------+--------------+
| name | name |
+--------+--------------+
| jason | 技术 |
| dragon | 人力资源 |
| kevin | 人力资源 |
| nick | 销售 |
| owen | 运营 |
+--------+--------------+
2. left join
left join 是左连接，以左表为基准，展示所有的数据，没有对应则用NULL代替(表1 left join 表2 on 连接条件)
mysql> select * from emp1 left join dep1 on emp1.dep_id = dep1.id;
+----+--------+--------+------+--------+------+--------------+
| id | name | gender | age | dep_id | id | name |
+----+--------+--------+------+--------+------+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | dragon | female | 48 | 201 | 201 | 人力资源 |
| 3 | kevin | male | 18 | 201 | 201 | 人力资源 |
| 4 | nick | male | 28 | 202 | 202 | 销售 |
| 5 | owen | male | 18 | 203 | 203 | 运营 |
| 6 | jerry | female | 18 | 204 | NULL | NULL |
+----+--------+--------+------+--------+------+--------------+
3.right join
right join 是右连接，以右表为基准，展示所有的数据，没有对应则用NULL代替(表1 right join 表2 on 连接条件)
mysql> select * from emp1 right join dep1 on emp1.dep_id = dep1.id;
+------+--------+--------+------+--------+-----+--------------+
| id | name | gender | age | dep_id | id | name |
+------+--------+--------+------+--------+-----+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | dragon | female | 48 | 201 | 201 | 人力资源 |
| 3 | kevin | male | 18 | 201 | 201 | 人力资源 |
| 4 | nick | male | 28 | 202 | 202 | 销售 |
| 5 | owen | male | 18 | 203 | 203 | 运营 |
| NULL | NULL | NULL | NULL | NULL | 205 | 安保 |
+------+--------+--------+------+--------+-----+--------------+
4.union
union 是全连接， 是左右连接的结合体，中间用union拼接
mysql> select * from emp1 left join dep1 on emp1.dep_id = dep1.id
-> union
-> select * from emp1 right join dep1 on emp1.dep_id = dep1.id;
+------+--------+--------+------+--------+------+--------------+
| id | name | gender | age | dep_id | id | name |
+------+--------+--------+------+--------+------+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | dragon | female | 48 | 201 | 201 | 人力资源 |
| 3 | kevin | male | 18 | 201 | 201 | 人力资源 |
| 4 | nick | male | 28 | 202 | 202 | 销售 |
| 5 | owen | male | 18 | 203 | 203 | 运营 |
| 6 | jerry | female | 18 | 204 | NULL | NULL |
| NULL | NULL | NULL | NULL | NULL | 205 | 安保 |
+------+--------+--------+------+--------+------+--------------+
作业
1.查询岗位名以及岗位包含的所有员工名字
mysql> select post as '部门',group_concat(name) as '姓名' from emp group by post;
+-----------------------------+------------------------------------------------+
| 部门 | 姓名 |
+-----------------------------+------------------------------------------------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,僧龙 |
| sale | 拉拉,乐乐,西西,呵呵,哈哈 |
| teacher | sank,jenny,jack,owen,tony,kevin,tom |
| 浦东第一帅形象代言 | jason |
+-----------------------------+------------------------------------------------+
2.查询岗位名以及各岗位内包含的员工个数
mysql> select post as '部门',count(id) as '员工人数' from emp group by post;
+-----------------------------+--------------+
| 部门 | 员工人数 |
+-----------------------------+--------------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 浦东第一帅形象代言 | 1 |
+-----------------------------+--------------+
3.查询公司内男员工和女员工的个数
mysql> select sex as '性别',count(id) as '员工人数' from emp group by sex;
+--------+--------------+
| 性别 | 员工人数 |
+--------+--------------+
| male | 10 |
| female | 8 |
+--------+--------------+
2 rows in set (0.00 sec)
4.查询岗位名以及各岗位的平均薪资
mysql> select post as '岗位',avg(salary) as '平均薪资' from emp group by post;
+-----------------------------+---------------+
| 岗位 | 平均薪资 |
+-----------------------------+---------------+
| operation | 16800.026000 |
| sale | 2600.294000 |
| teacher | 151842.901429 |
| 浦东第一帅形象代言 | 7300.330000 |
+-----------------------------+---------------+
5.查询岗位名以及各岗位的最高薪资
mysql> select post as '岗位',max(salary) as '最高薪资' from emp group by post;
+-----------------------------+--------------+
| 岗位 | 最高薪资 |
+-----------------------------+--------------+
| operation | 20000.00 |
| sale | 4000.33 |
| teacher | 1000000.31 |
| 浦东第一帅形象代言 | 7300.33 |
+-----------------------------+--------------+
6.查询岗位名以及各岗位的最低薪资
mysql> select post as '岗位',min(salary) as '最低工资' from emp group by post;
+-----------------------------+--------------+
| 岗位 | 最低工资 |
+-----------------------------+--------------+
| operation | 10000.13 |
| sale | 1000.37 |
| teacher | 2100.00 |
| 浦东第一帅形象代言 | 7300.33 |
+-----------------------------+--------------+
7.查询男员工与男员工的平均薪资，女员工与女员工的平均薪资
mysql> select sex as '性别',avg(salary) as '平均薪资' from emp group by sex;
+--------+---------------+
| 性别 | 平均薪资 |
+--------+---------------+
| male | 110920.077000 |
| female | 7250.183750 |
+--------+---------------+
8.统计各部门年龄在30岁以上的员工平均工资
mysql> select post as '部门',avg(salary) as '平均薪资' from emp where age >= 30 group by post;
+---------+---------------+
| 部门 | 平均薪资 |
+---------+---------------+
| sale | 2500.240000 |
| teacher | 255450.077500 |
+---------+---------------+
9.统计各部门年龄在10岁以上的员工平均工资，并且保留平均工资大于1000的部门，然后对平均工资进行排序
mysql> select post as '部门',avg(salary) as '平均工资' from emp where age >10 group by post having avg(salary) >1000 order by avg(salary);
+-----------------------------+---------------+
| 部门 | 平均工资 |
+-----------------------------+---------------+
| sale | 2600.294000 |
| 浦东第一帅形象代言 | 7300.330000 |
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------------------------+---------------+
