mysql关键字与连表操作理论
2024-05-26 11:20:41
1、关键字
重点中的重点：关键字的执行优先级fromwheregroup byhavingselectdistinctorder bylimit1.找到表:from2.拿着where指定的约束条件，去文件/表中取出一条条记录3.将取出的一条条记录进行分组group by，如果没有group by，则整体作为一组4.将分组的结果进行having过滤5.执行select6.去重7.将结果按条件排序：order by8.限制结果的显示条数
- 前期表准备
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
);#插入记录
#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','张江第一帅形象代言',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);mysql> select * from emp;
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 1 | jason | male | 18 | 2017-03-01 | 张江第一帅形象代言 | 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 |
| 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 |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
# 当表字段特别多 展示的时候错乱 可以使用\G分行展示
select * from emp\G;# 个别同学的电脑在插入中文的时候还是会出现乱码或者空白的现象 你可以将字符编码统一设置成GBK
- where 筛选条件
# 作用:是对整体数据的一个筛选操作
# 1.查询id大于等于3小于等于6的数据
select id,name,age from emp where id>=3 and id<=6;
select id,name from emp where id between 3 and 6; 两者等价
'''
mysql> select id,name,age from emp where id >=3 and id <= 6;
+----+-------+-----+
| id | name | age |
+----+-------+-----+
| 3 | kevin | 81 |
| 4 | tony | 73 |
| 5 | owen | 28 |
| 6 | jack | 18 |
+----+-------+-----+
'''
# 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;
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字母o的员工的姓名和薪资
"""
模糊查询like% 匹配任意多个字符_ 匹配任意单个字符
"""
select name,salary from emp where name like '%o%';
'''
mysql> select name,salary from emp where name like '%o%';
+-------+------------+
| name | salary |
+-------+------------+
| jason | 7300.33 |
| tom | 1000000.31 |
| tony | 3500.00 |
| owen | 2100.00 |
+-------+------------+
'''
# 4.查询员工姓名是由四个字符组成的 姓名和薪资 char_length() _
select name,salary from emp where name like '____';
select name,salary from emp where char_length(name) = 4;
'''
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id大于6的数据
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 | 张江第一帅形象代言 | 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 | 张江第一帅形象代言 | 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姓名和岗位名 针对null不用等号 用is
select name,post from emp where post_comment = NULL;
'''
mysql> select name,post from emp where post_comment=NULL;
Empty set (0.00 sec)
'''
select name,post from emp where post_comment is NULL;
'''
mysql> select name,post from emp where post_comment is NULL;
+-----------+-----------------------------+
| name | post |
+-----------+-----------------------------+
| jason | 张江第一帅形象代言 |
| 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 |
+-----------+-----------------------------+
'''- group by分组
# 分组实际应用场景 分组应用场景非常的多男女比例部门平均薪资部门秃头率国家之间数据统计# 1 按照部门分组
select * from emp group by post;
"""
分组之后 最小可操作单位应该是组 不再是组内的单个数据上述命令在你没有设置严格模式的时候是可正常执行的 返回的是分组之后 每个组的第一条数据 但是这不符合分组的规范:分组之后不应该考虑单个数据 而应该以组为操作单位(分组之后 没办法直接获取组内单个数据)如果设置了严格模式 那么上述命令会直接报错
"""
set global sql_mode = 'strict_trans_tables,only_full_group_by';设置严格模式之后 分组 默认只能拿到分组的依据
select post from emp group by post;
'''
mysql> select * from emp group by post;
ERROR 1055 (42000): 'day47.emp.id' isn't in GROUP BY
'''
按照什么分组就只能拿到分组 其他字段不能直接获取 需要借助于一些方法(聚合函数)"""
什么时候需要分组啊？？？关键字 每个 平均 最高 最低 聚合函数max #最大min #最小sum #求和count #计数avg #平均
"""
# 1.获取每个部门的最高薪资
select post,max(salary) from emp group by post;
'''
mysql> select post,max(salary) from emp group by post;
+-----------------------------+-------------+
| post | max(salary) |
+-----------------------------+-------------+
| operation | 20000.00 |
| sale | 4000.33 |
| teacher | 1000000.31 |
| 张江第一帅形象代言 | 7300.33 |
+-----------------------------+-------------+
'''
select post as '部门',max(salary) as '最高薪资' from emp group by post;
select post '部门',max(salary) '最高薪资' from emp group by post;
'''
mysql> select post as '部门',max(salary) as '最高薪资' from emp group by post;
+-----------------------------+--------------+
| 部门 | 最高薪资 |
+-----------------------------+--------------+
| operation | 20000.00 |
| sale | 4000.33 |
| teacher | 1000000.31 |
| 张江第一帅形象代言 | 7300.33 |
+-----------------------------+--------------+
'''
# as可以给字段起别名 也可以直接省略不写 但是不推荐 因为省略的话语意不明确 容易错乱# 2.获取每个部门的最低薪资
select post,min(salary) from emp group by post;
'''
mysql> select post,min(salary) from emp group by post;
+-----------------------------+-------------+
| post | min(salary) |
+-----------------------------+-------------+
| operation | 10000.13 |
| sale | 1000.37 |
| teacher | 2100.00 |
| 张江第一帅形象代言 | 7300.33 |
+-----------------------------+-------------+
'''
# 3.获取每个部门的平均薪资
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 |
| 张江第一帅形象代言 | 7300.330000 |
+-----------------------------+---------------+
'''
# 4.获取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 |
| 张江第一帅形象代言 | 7300.33 |
+-----------------------------+-------------+
'''
# 5.获取每个部门的人数
select post,count(id) from emp group by post; # 常用 符合逻辑
select post,count(salary) from emp group by post;
select post,count(age) from emp group by post;
'''
mysql> select post,count(id) from emp group by post;
+-----------------------------+-----------+
| post | count(id) |
+-----------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 张江第一帅形象代言 | 1 |
+-----------------------------+-----------+
'''
select post,count(post_comment) from emp group by post; null不行
'''
mysql> select post,count(post_comment) from emp group by post;
+-----------------------------+---------------------+
| post | count(post_comment) |
+-----------------------------+---------------------+
| operation | 0 |
| sale | 0 |
| teacher | 0 |
| 张江第一帅形象代言 | 0 |
+-----------------------------+---------------------+
'''
# 6.查询分组之后的部门名称和每个部门下所有的员工姓名
# group_concat不单单可以支持你获取分组之后的其他字段值 还支持拼接操作
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 |
| 张江第一帅形象代言 | jason |
+-----------------------------+------------------------------------------------+
'''
#进行拼接操作
select post,group_concat(name,'_DDD') from emp group by post;
'''
mysql> select post,group_concat(name,'_DDD') from emp group by post;
+-----------------------------+--------------------------------------------------------------------+
| post | group_concat(name,'_DDD') |
+-----------------------------+--------------------------------------------------------------------+
| operation | 程咬铁_DDD,程咬铜_DDD,程咬银_DDD,程咬金_DDD,僧龙_DDD |
| sale | 拉拉_DDD,乐乐_DDD,西西_DDD,呵呵_DDD,哈哈_DDD |
| teacher | sank_DDD,jenny_DDD,jack_DDD,owen_DDD,tony_DDD,kevin_DDD,tom_DDD |
| 张江第一帅形象代言 | jason_DDD |
+-----------------------------+--------------------------------------------------------------------+
'''
#进行字段内容拼接
select post,group_concat(name,':',salary) from emp group by post;
'''
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 |
| 张江第一帅形象代言 | jason:7300.33 |
+-----------------------------+--------------------------------------------------------------------------------------------------+
4 rows in set (0.00 sec)
'''concat不分组的时候用 select concat('NAME:',name),concat('SAL:',salary) from emp;
'''
mysql> select concat('NAME:',name),concat('SAL:',salary) from emp;
+----------------------+-----------------------+
| concat('NAME:',name) | concat('SAL:',salary) |
+----------------------+-----------------------+
| NAME:jason | SAL:7300.33 |
| NAME:tom | SAL:1000000.31 |
| NAME:kevin | SAL:8300.00 |
| NAME:tony | SAL:3500.00 |
| NAME:owen | SAL:2100.00 |
| NAME:jack | SAL:9000.00 |
| NAME:jenny | SAL:30000.00 |
| NAME:sank | SAL:10000.00 |
| NAME:哈哈 | SAL:3000.13 |
| NAME:呵呵 | SAL:2000.35 |
| NAME:西西 | SAL:1000.37 |
| NAME:乐乐 | SAL:3000.29 |
| NAME:拉拉 | SAL:4000.33 |
| NAME:僧龙 | SAL:10000.13 |
| NAME:程咬金 | SAL:20000.00 |
| NAME:程咬银 | SAL:19000.00 |
| NAME:程咬铜 | SAL:18000.00 |
| NAME:程咬铁 | SAL:17000.00 |
+----------------------+-----------------------+
'''
# 补充 as语法不单单可以给字段起别名 还可以给表临时起别名
select emp.id,emp.name from emp;
select emp.id,emp.name from emp as t1; 报错
select t1.id,t1.name from emp as t1;# 查询每个人的年薪 12薪
select name,salary*12 from emp;'''
mysql> select name,salary*12 from emp;
+-----------+-------------+
| name | salary*12 |
+-----------+-------------+
| jason | 87603.96 |
| tom | 12000003.72 |
| kevin | 99600.00 |
| tony | 42000.00 |
| owen | 25200.00 |
| jack | 108000.00 |
| jenny | 360000.00 |
| sank | 120000.00 |
| 哈哈 | 36001.56 |
| 呵呵 | 24004.20 |
| 西西 | 12004.44 |
| 乐乐 | 36003.48 |
| 拉拉 | 48003.96 |
| 僧龙 | 120001.56 |
| 程咬金 | 240000.00 |
| 程咬银 | 228000.00 |
| 程咬铜 | 216000.00 |
| 程咬铁 | 204000.00 |
+-----------+-------------+
'''
- 分组注意事项
# 关键字where和group by同时出现的时候group by必须在where的后面
where先对整体数据进行过滤之后再分组操作
where筛选条件不能使用聚合函数
select id,name,age from emp where max(salary) > 3000;
select max(salary) from emp; # 不分组 默认整体就是一组
# 统计各部门年龄在30岁以上的员工平均薪资1 先求所有年龄大于30岁的员工select * from emp where age>30;2 再对结果进行分组select * from emp where age>30 group by post;select post,avg(salary) from emp where age>30 group by post;
'''
mysql> select post,avg(salary)from emp where age>30 group by post;
+---------+---------------+
| post | avg(salary) |
+---------+---------------+
| sale | 2500.240000 |
| teacher | 255450.077500 |
+---------+---------------+
'''
- having分组之后的筛选条件
"""
having的语法根where是一致的
只不过having是在分组之后进行的过滤操作
即having是可以直接使用聚合函数的
"""
# 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薪资大于10000的部门
select post,avg(salary) from emp where age>30 group by posthaving avg(salary) > 10000;
'''
mysql> select post,avg(salary) from emp where age >30 group by post having avg(salary) >10000;
+---------+---------------+
| post | avg(salary) |
+---------+---------------+
| teacher | 255450.077500 |
+---------+---------------+
'''
- distinct去重
一定要注意 必须是完全一样的数据才可以去重！！！
一定不要将主键忽视了 有主键存在的情况下 是不可能去重的
#不能成功去重[
{'id':1,'name':'jason','age':18},
{'id':2,'name':'jason','age':18},
{'id':3,'name':'egon','age':18}
]select distinct id,age from emp; #包含主键，不会成功去重
'''
mysql> select distinct id,age from emp;+----+-----+
| id | age |
+----+-----+
| 1 | 18 |
| 2 | 78 |
| 3 | 81 |
| 4 | 73 |
| 5 | 28 |
| 6 | 18 |
| 7 | 18 |
| 8 | 48 |
| 9 | 48 |
| 10 | 38 |
| 11 | 18 |
| 12 | 18 |
| 13 | 28 |
| 14 | 28 |
| 15 | 18 |
| 16 | 18 |
| 17 | 18 |
| 18 | 18 |
+----+-----+
'''
select distinct age from emp;'''
mysql> select distinct age from emp;
+-----+
| age |
+-----+
| 18 |
| 78 |
| 81 |
| 73 |
| 28 |
| 48 |
| 38 |
+
'''
- order by排序
select * from emp order by salary;
select * from emp order by salary asc;
select * from emp order by salary desc;
"""
order by默认是升序 asc 该asc可以省略不写
也可以修改为降序 desc
"""
# 先按照age降序排 如果碰到age相同 则再按照salary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 | 张江第一帅形象代言 | 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 |
+----+-----------+--------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
'''# 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薪资大于1000的部门,然后对平均工资降序排序select post,avg(salary) from emp where age>10 group by posthaving avg(salary) > 1000order by avg(salary) desc;'''
mysql> select post,avg(salary) from emp-> where age>10-> group by post-> having avg(salary) > 1000-> order by avg(salary) desc-> ;
+-----------------------------+---------------+
| post | avg(salary) |
+-----------------------------+---------------+
| teacher | 151842.901429 |
| operation | 16800.026000 |
| 张江第一帅形象代言 | 7300.330000 |
| sale | 2600.294000 |
+-----------------------------+---------------+
4 rows in set (0.00 sec)
'''
- limit限制展示条数
select * from emp;
"""针对数据过多的情况 我们通常都是做分页处理"""
select * from emp limit 3; # 只展示三条数据select * from emp limit 0,5;
'''
mysql> select * from emp limit 0,5;
+----+-------+------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-------+------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
| 1 | jason | male | 18 | 2017-03-01 | 张江第一帅形象代言 | 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 |
+----+-------+------+-----+------------+-----------------------------+--------------+------------+--------+-----------+
'''
select * from emp limit 5,5;'''
mysql> select * from emp limit 5,5;
+----+--------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+--------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| 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 |
+----+--------+--------+-----+------------+---------+--------------+----------+--------+-----------+
'''
第一个参数是起始位置
第二个参数是展示条数
- 正则
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 | 张江第一帅形象代言 | NULL | 7300.33 | 401 | 1 |
| 7 | jenny | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
+----+-------+------+-----+------------+-----------------------------+--------------+----------+--------+-----------+
'''
2、多表操作
- 前期表准备
#建表
create table dep(
id int,
name varchar(20)
);create table emp(
id int primary key auto_increment,
name varchar(20),
sex enum('male','female') not null default 'male',
age int,
dep_id int
);#插入数据
insert into dep values
(200,'技术'),
(201,'人力资源'),
(202,'销售'),
(203,'运营');
(205,'行政')insert into emp(name,sex,age,dep_id) values
('jason','male',18,200),
('egon','female',48,201),
('kevin','male',18,201),
('nick','male',28,202),
('owen','male',18,203),
('jerry','female',18,204);
- 表查询
select * from dep;
'''
mysql> select * from dep;
+------+--------------+
| id | name |
+------+--------------+
| 200 | 技术 |
| 201 | 人力资源 |
| 202 | 销售 |
| 203 | 运营 |
| 205 | 行政 |
+------+--------------+
'''
select * from emp;
'''
mysql> select * from emp;
+----+-------+--------+------+--------+
| id | name | sex | age | dep_id |
+----+-------+--------+------+--------+
| 1 | jason | male | 18 | 200 |
| 2 | egon | female | 48 | 201 |
| 3 | kevin | male | 18 | 201 |
| 4 | nick | male | 28 | 202 |
| 5 | owen | male | 18 | 203 |
| 6 | jerry | female | 18 | 204 |
+----+-------+--------+------+--------+
'''
select * from dep,emp; # 结果 笛卡尔积
'''
mysql> select * from dep,emp;
+------+--------------+----+-------+--------+------+--------+
| id | name | id | name | sex | age | dep_id |
+------+--------------+----+-------+--------+------+--------+
| 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 | 行政 | 1 | jason | male | 18 | 200 |
| 200 | 技术 | 2 | egon | female | 48 | 201 |
| 201 | 人力资源 | 2 | egon | female | 48 | 201 |
| 202 | 销售 | 2 | egon | female | 48 | 201 |
| 203 | 运营 | 2 | egon | female | 48 | 201 |
| 205 | 行政 | 2 | egon | female | 48 | 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 | 行政 | 3 | kevin | male | 18 | 201 |
| 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 | 行政 | 4 | nick | male | 28 | 202 |
| 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 | 行政 | 5 | owen | male | 18 | 203 |
| 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 | 行政 | 6 | jerry | female | 18 | 204 |
+------+--------------+----+-------+--------+------+--------+
'''select * from emp,dep where emp.dep_id = dep.id;
'''
mysql> select * from emp,dep where emp.dep_id = dep.id;
+----+-------+--------+------+--------+------+--------------+
| id | name | sex | age | dep_id | id | name |
+----+-------+--------+------+--------+------+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | egon | 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也知道 你在后面查询数据过程中 肯定会经常用到拼表操作
所以特地给你开设了对应的方法inner join 内连接left join 左连接right join 右连接union 全连接
"""
# inner join 内连接
select * from emp inner join dep on emp.dep_id = dep.id;
# 只拼接两张表中公有的数据部分
'''
mysql> select * from emp inner join dep on emp.dep_id = dep.id;
+----+-------+--------+------+--------+------+--------------+
| id | name | sex | age | dep_id | id | name |
+----+-------+--------+------+--------+------+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | egon | 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 |
+----+-------+--------+------+--------+------+--------------+
'''
# left join 左连接
select * from emp left join dep on emp.dep_id = dep.id;
# 左表所有的数据都展示出来 没有对应的项就用NULL
'''
mysql> select * from emp left join dep on emp.dep_id = dep.id;
+----+-------+--------+------+--------+------+--------------+
| id | name | sex | age | dep_id | id | name |
+----+-------+--------+------+--------+------+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | egon | 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 |
+----+-------+--------+------+--------+------+--------------+
'''
# right join 右连接
select * from emp right join dep on emp.dep_id = dep.id;
# 右表所有的数据都展示出来 没有对应的项就用NULL
'''
mysql> select * from emp right join dep on emp.dep_id = dep.id;
+------+-------+--------+------+--------+------+--------------+
| id | name | sex | age | dep_id | id | name |
+------+-------+--------+------+--------+------+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | egon | 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 | 行政 |
+------+-------+--------+------+--------+------+--------------+
'''# union 全连接 左右两表所有的数据都展示出来
select * from emp left join dep on emp.dep_id = dep.id
union
select * from emp right join dep on emp.dep_id = dep.id;'''
mysql> select * from emp left join dep on emp.dep_id = dep.id-> union-> select * from emp right join dep on emp.dep_id = dep.id;
+------+-------+--------+------+--------+------+--------------+
| id | name | sex | age | dep_id | id | name |
+------+-------+--------+------+--------+------+--------------+
| 1 | jason | male | 18 | 200 | 200 | 技术 |
| 2 | egon | 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 | 行政 |
+------+-------+--------+------+--------+------+--------------+
'''
- 子查询
"""
子查询就是我们平时解决问题的思路分步骤解决问题第一步第二步...
将一个查询语句的结果当做另外一个查询语句的条件去用
"""
# 查询部门是技术或者人力资源的员工信息1 先获取部门的id号2 再去员工表里面筛选出对应的员工select id from dep where name='技术' or name = '人力资源';select name from emp where dep_id in (200,201);select * from emp where dep_id in (select id from dep where name='技术' or name = '人力资源');'''
mysql> select * from emp where dep_id in (select id from dep where name='技术' or name = '人力资源');
+----+-------+--------+------+--------+
| id | name | sex | age | dep_id |
+----+-------+--------+------+--------+
| 1 | jason | male | 18 | 200 |
| 2 | egon | female | 48 | 201 |
| 3 | kevin | male | 18 | 201 |
+----+-------+--------+------+--------+
'''
总结
表的查询结果可以作为其他表的查询条件
也可以通过起别名的方式把它作为一个张虚拟表根其他表关联"""
多表查询就两种方式先拼接表再查询子查询 一步一步来
"""
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