day41

今日内容概要

• 创建表的完整语法

• 约束条件(在数据类型的基础上在进行约束)

  • unsigned

  • zerofill

  • default

  • not null

  • unique

  • primary key

  • auto_increment

• 补充一些别的SQL语句

• 其他查询关键字

  • select

  • from

  • where

  • order by

  • limit

  • having

  • regexp

  • and or in not in between and like 等

创建表的完整语法

create table t1(id int, name varchar(43), age int);

create table 库名.表名（字段名 数据类型 约束条件，字段名1 数据类型 约束条件)；

insert into 库民.表名 values（1，2）；

1.字段名和数据类型是必须写的，不能忽略
2.约束条件是可选的，可有可无，而且有多个
3.表结构中最一个字段不能有逗号

约束条件

约束条件其实就是在数据类型的基础之上在做约束
1.unsigened (无符号)

mysql> create table t1(id int unsigned);
Query OK, 0 rows affected (0.04 sec)

mysql> insert into t1 values(-10);
ERROR 1264 (22003): Out of range value for column 'id' at row 1
mysql> insert into t1 values(10);
Query OK, 1 row affected (0.01 sec)

mysql> select * from t1;
+------+
| id   |
+------+
|   10 |
+------+
1 row in set (0.00 sec)

mysql>

2.zerofill (0填充）

mysql> create table t2(id int(5) zerofill);
Query OK, 0 rows affected (0.04 sec)

mysql> insert into t2 values(123);
Query OK, 1 row affected (0.00 sec)

mysql> select * from t2;
+-------+
| id    |
+-------+
| 00123 |
+-------+
1 row in set (0.00 sec)

mysql>

3.default (默认值）

mysql> create table t3(id int,name varchar(32) default 'wzc');
Query OK, 0 rows affected (0.02 sec)

mysql> insert into t3(id) values(1);
Query OK, 1 row affected (0.00 sec)

mysql> select * from t3;
+------+------+
| id   | name |
+------+------+
|    1 | wzc  |
+------+------+
1 row in set (0.00 sec)

4.not null(非空）

mysql> create table t4(id int,name varchar(32) not null);
Query OK, 0 rows affected (0.02 sec)

mysql> insert into t4(id) values(1);
ERROR 1364 (HY000): Field 'name' doesn't have a default value
mysql> select * from t4;
Empty set (0.00 sec)

5.unique(唯一）
单列唯一

mysql> create table t5(id int,name varchar(32) unique);
Query OK, 0 rows affected (0.02 sec)

mysql> insert into t5 values(1,'wzc');
Query OK, 1 row affected (0.00 sec)

mysql> insert into t5 values(2,'wzc');
ERROR 1062 (23000): Duplicate entry 'wzc' for key 'name'

多列唯一

mysql> create table t6(id int, ip varchar(32),port varchar(32),unique(ip,port));
Query OK, 0 rows affected (0.03 sec)

mysql> insert into t6 values(1,'192.168.150.1',3306);
Query OK, 1 row affected (0.01 sec)

mysql> insert into t6 values(1,'192.168.150.1',3307);
Query OK, 1 row affected (0.00 sec)

mysql> insert into t6 values(1,'192.168.150.2',3307);
Query OK, 1 row affected (0.00 sec)

mysql> insert into t6 values(1,'192.168.150.2',3307);
ERROR 1062 (23000): Duplicate entry '192.168.150.2-3307' for key 'ip'

6.primary key(主键）
主键单纯从约束上来看，它相当于是非空且唯一

mysql> create table t7(id int primary key);
Query OK, 0 rows affected (0.04 sec)

mysql> desc t7;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | NO   | PRI | NULL    |       |
+-------+---------+------+-----+---------+-------+
1 row in set (0.02 sec)

主键本身是一种索引，索引能够加快查询速度

InnoDB存储引擎规定每一张表都要有一个主键，但是，我之前创建的表都没有指定主键，表是怎么创建成功的？
是因为InnoDB存储引擎内部有一个隐藏的主键，这个主键我们看不到，它也不能够加快查询速度，仅仅是为了帮助我们把表创建成功，所以，以后我们创建表的时候都主动的创建一个主键，我们自己创建的主键能够加快查询速度，因为是一个索引。
一般情况下，主键应该创建id字段，一张表中不只是有一个主键，可以有多个主键，但是，大多数情况下，都只有一个

7.auto_incrment(自增）

每一次主动比上一次加一，一般情况下配合主键使用

mysql> create table t8(id int primary key auto_increment,name varchar(32));
Query OK, 0 rows affected (0.03 sec)

mysql> insert into t8(name) values('wzc');
Query OK, 1 row affected (0.01 sec)

mysql> insert into t8(name) values('wzc');
Query OK, 1 row affected (0.00 sec)

mysql> select * from t8;
+----+------+
| id | name |
+----+------+
|  1 | wzc  |
|  2 | wzc  |
+----+------+
2 rows in set (0.00 sec)

mysql> delete from t8 where id=2;
Query OK, 1 row affected (0.00 sec)

mysql> insert into t8(name) values('wzc');
Query OK, 1 row affected (0.00 sec)

mysql> select * from t8;
+----+------+
| id | name |
+----+------+
|  1 | wzc  |
|  3 | wzc  |
+----+------+
2 rows in set (0.00 sec)

补充一些sql语句

1.增加字段

mysql> desc t9;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(9)      | YES  |     | NULL    |       |
| name  | varchar(32) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.02 sec)

mysql> alter table t9 add age varchar(32);
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc t9;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(9)      | YES  |     | NULL    |       |
| name  | varchar(32) | YES  |     | NULL    |       |
| age   | varchar(32) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.02 sec)

mysql> alter table t9 add age varchar(32) after id;# 增加在指定字段后
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc t9;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(9)      | YES  |     | NULL    |       |
| age   | varchar(32) | YES  |     | NULL    |       |
| name  | varchar(32) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.02 sec)

mysql> alter table t9 add gender varchar(32) first;# 增加在最前面
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc t9;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| gender | varchar(32) | YES  |     | NULL    |       |
| id     | int(9)      | YES  |     | NULL    |       |
| age    | varchar(32) | YES  |     | NULL    |       |
| name   | varchar(32) | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+
4 rows in set (0.01 sec)

2.删除字段

mysql> desc t9;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(9)      | YES  |     | NULL    |       |
| name  | varchar(32) | YES  |     | NULL    |       |
| age   | varchar(32) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.02 sec)

mysql> alter table t9 drop age;
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc t9;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(9)      | YES  |     | NULL    |       |
| name  | varchar(32) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.02 sec)

4.修改字段名 
modify：只能改字段数据类型完整约束，不能改字段名（数据类型可改范围）
change：可以改字段名

mysql> alter table t9 modify age varchar(64);
Query OK, 1 row affected (0.07 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> desc t9;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| gender | varchar(32) | YES  |     | NULL    |       |
| id     | int(9)      | YES  |     | NULL    |       |
| age    | varchar(64) | YES  |     | NULL    |       |
| name   | varchar(32) | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+
4 rows in set (0.02 sec)

mysql> alter table t9 change name hobby varchar(32);
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc t9;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| gender | varchar(32) | YES  |     | NULL    |       |
| id     | int(9)      | YES  |     | NULL    |       |
| age    | varchar(64) | YES  |     | NULL    |       |
| hobby  | varchar(32) | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+
4 rows in set (0.02 sec)

数据准备

create table emp(
  id int primary key auto_increment,
  name varchar(20) not null,
  sex enum('male','female') not null default 'male', #大部分是男的
  age smallint(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
);

insert into emp(name,sex,age,hire_date,post,salary,office,depart_id) values
('tom','male',78,'20150302','teacher',1000000.31,401,1),#以下是教学部
('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where

1.查询id大于等于3小于等于6的数据

mysql> select * from emp where id >= 3 and id <= 6;
+----+-------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name  | sex    | age | hire_date  | post    | post_comment | salary   | office | depart_id |
+----+-------+--------+-----+------------+---------+--------------+----------+--------+-----------+
|  3 | tony  | male   |  73 | 2014-07-01 | teacher | NULL         |  3500.00 |    401 |         1 |
|  4 | owen  | male   |  28 | 2012-11-01 | teacher | NULL         |  2100.00 |    401 |         1 |
|  5 | jack  | female |  18 | 2011-02-11 | teacher | NULL         |  9000.00 |    401 |         1 |
|  6 | jenny | male   |  18 | 1900-03-01 | teacher | NULL         | 30000.00 |    401 |         1 |
+----+-------+--------+-----+------------+---------+--------------+----------+--------+-----------+
4 rows in set (0.00 sec)

mysql> select * from emp where id between 3 and 6;
+----+-------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name  | sex    | age | hire_date  | post    | post_comment | salary   | office | depart_id |
+----+-------+--------+-----+------------+---------+--------------+----------+--------+-----------+
|  3 | tony  | male   |  73 | 2014-07-01 | teacher | NULL         |  3500.00 |    401 |         1 |
|  4 | owen  | male   |  28 | 2012-11-01 | teacher | NULL         |  2100.00 |    401 |         1 |
|  5 | jack  | female |  18 | 2011-02-11 | teacher | NULL         |  9000.00 |    401 |         1 |
|  6 | jenny | male   |  18 | 1900-03-01 | teacher | NULL         | 30000.00 |    401 |         1 |
+----+-------+--------+-----+------------+---------+--------------+----------+--------+-----------+
4 rows in set (0.00 sec)

2.查询薪资是20000或者18000或者17000的数据

mysql> select * from emp where salary = 20000 or salary = 18000 or salary = 17000;

mysql> select * from emp where salary in (20000,18000,17000);

3.查询员工姓名中包含o字母的员工姓名和薪资
在你刚接触mysql查询的时候，建议你按照查询的优先级顺序拼写出你的aql语句
先是查哪张表 from emp
再是根据什么条件去查 where name like ‘%o%’
再是对查询出来的数据筛选展示部分 select name,salary

mysql> select name,salary from emp where name like '%o%';
+------+------------+
| name | salary     |
+------+------------+
| tom  | 1000000.31 |
| tony |    3500.00 |
| owen |    2100.00 |
+------+------------+
3 rows in set (0.00 sec)

 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 like '____';

mysql> select name,salary from emp where char_length(name) = 4;

 5.查询id小于3或者大于6的数据

mysql> select * from emp where id < 3 or id > 6;

mysql> select * from emp where id not between 3 and 6;

 6.查询薪资不在20000，18000，17000范围的数据

mysql> select * from emp where salary not in (20000,18000,17000);

7.查询岗位描述为空的员工名与岗位名  针对null不能用等号，只能用is

mysql> select name,post from emp where post_comment is NULL;

查询关键字之group by分组

分组：按照某个指定的条件将单个单个的个体分成一个个整体
单纯的分组是没有意义的
再MySQL中分组之后，只能够获得分组的依据！按照哪个字段分组就只能获取这个字段的值，别的字段不能拿到

分组一般配合聚合函数使用：sum max min avg count
分组的关键字：group by
1.分组之后默认可以获取所有的字段信息
2.分组之后，展示的数据都是每个组的第一条数据

1.按部门分组

mysql> select * from emp group by post;

mysql> select post from emp group by post;# 查看分组

2.获取每个部门的最高工资

mysql> select post,max(salary) from emp group by post;

补充：在显示的时候还可以给字段取别名

mysql> select post '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 |
+-----------+--------------+
3 rows in set (0.00 sec)

 每个部门的最低工资

mysql> select post,min(salary) from emp group by post;

每个部门的平均工资

mysql> select post,avg(salary) from emp group by post;

每个部门的工资总和

mysql> select post,sum(salary) from emp group by post;

每个部门的人数

mysql> select post,count(id) from emp group by post;

分组补充函数

如果真的需要获取分组以外的数据字段，可以使用group_concat()，分组之后使用
每个部门的员工姓名

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            |
+-----------+------------------------------------------------+
3 rows in set (0.00 sec)

mysql> select post,group_concat(name,'|',sex) from emp group by post;

mysql> select post,group_concat(name,'|',sex,'|',post) from emp group by post;

mysql> select post,group_concat(distinct name ) from emp group by post;
+-----------+------------------------------------------------+
| post      | group_concat(distinct 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            |
+-----------+------------------------------------------------+

mysql> select post,group_concat(distinct name separator '%') from emp group by post;

concat 不分组使用

mysql> select concat(name,sex) from emp;
+------------------+
| concat(name,sex) |
+------------------+
| tommale          |
| kevinmale        |
| tonymale         |
| owenmale         |
| jackfemale       |
| jennymale        |
| sankmale         |
| 哈哈female       |
| 呵呵female       |
| 西西female       |
| 乐乐female       |
| 拉拉female       |
| 僧龙male         |
| 程咬金male       |
| 程咬银female     |
| 程咬铜male       |
| 程咬铁female     |
+------------------+
17 rows in set (0.00 sec)

select concat(name,'|', sex) from emp;

concat_ws()

mysql> select post,concat_ws('|',name,age,sex)from emp;
+-----------+-----------------------------+
| post      | concat_ws('|',name,age,sex) |
+-----------+-----------------------------+
| teacher   | tom|78|male                 |
| teacher   | kevin|81|male               |
| teacher   | tony|73|male                |
| teacher   | owen|28|male                |
| teacher   | jack|18|female              |
| teacher   | jenny|18|male               |
| teacher   | sank|48|male                |
| sale      | 哈哈|48|female              |
| sale      | 呵呵|38|female              |
| sale      | 西西|18|female              |
| sale      | 乐乐|18|female              |
| sale      | 拉拉|28|female              |
| operation | 僧龙|28|male                |
| operation | 程咬金|18|male              |
| operation | 程咬银|18|female            |
| operation | 程咬铜|18|male              |
| operation | 程咬铁|18|female            |
+-----------+-----------------------------+
17 rows in set (0.00 sec)

关键字之having过滤

where与having都是筛选功能，但是有区别
where在分组之前对数据进行筛选
having在分组之后对数据进行筛选

1.统计各部门年龄在30岁以上的员工平均薪资,并且保留平均薪资大于10000的部门.

先筛选出年龄在30岁以上的
mysql> select * from emp where age > 30;
+----+--------+--------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name   | sex    | age | hire_date  | post    | post_comment | salary     | office | depart_id |
+----+--------+--------+-----+------------+---------+--------------+------------+--------+-----------+
|  1 | tom    | male   |  78 | 2015-03-02 | teacher | NULL         | 1000000.31 |    401 |         1 |
|  2 | kevin  | male   |  81 | 2013-03-05 | teacher | NULL         |    8300.00 |    401 |         1 |
|  3 | tony   | male   |  73 | 2014-07-01 | teacher | NULL         |    3500.00 |    401 |         1 |
|  7 | sank   | male   |  48 | 2010-11-11 | teacher | NULL         |   10000.00 |    401 |         1 |
|  8 | 哈哈   | female |  48 | 2015-03-11 | sale    | NULL         |    3000.13 |    402 |         2 |
|  9 | 呵呵   | female |  38 | 2010-11-01 | sale    | NULL         |    2000.35 |    402 |         2 |
+----+--------+--------+-----+------------+---------+--------------+------------+--------+-----------+
6 rows in set (0.00 sec)

再进行分组，按照部门分组
mysql> select avg(salary) as avg_salary from emp where age > 30 group by post;
+---------------+
| avg_salary    |
+---------------+
|   2500.240000 |
| 255450.077500 |
+---------------+
2 rows in set (0.00 sec)

保留平均薪资大于100000的部门
mysql> select avg(salary) as avg_salary from emp where age > 30 group by post having avg(salary) > 10000;
+---------------+
| avg_salary    |
+---------------+
| 255450.077500 |
+---------------+
1 row in set (0.00 sec)

 关键字之distinct去重

带主键的数据去重有没有意义？ 没有，主键本身就是唯一的

mysql> select distinct sex from emp;
+--------+
| sex    |
+--------+
| male   |
| female |
+--------+
2 rows in set (0.00 sec)

关键字之order by排序

select * from emp order by salary; # 默认升序排

select * from emp order by salary desc; # 降序排

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;

多字段排序，如果想让后面的字段排序生效，前提：前面的排序字段必须一样

统计各部门年龄在20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

20岁以上的员工
mysql> select * from emp where age >20;
各部门的平均薪资
mysql> select avg(salary) from emp where age > 20 group by post having avg(salary) >1000;

mysql> select avg(salary) from emp where age > 20 group by post having avg(salary) > 1000 order by avg(salary) desc;

关键字之limit分页

限制展示条数

mysql> select * from emp limit 3;

查询工资最高的人的详细信息
mysql> select * from emp order by salary desc limit 1;

分页显示
mysql> select * from emp limit 0,5; # 第一个参数表示起始位置，第二个参数表示的是条数，不是索引位置

关键字之regxp正则

mysql> select * from emp where name regexp '^j.*(n|y)$';
+----+-------+------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name  | sex  | age | hire_date  | post    | post_comment | salary   | office | depart_id |
+----+-------+------+-----+------------+---------+--------------+----------+--------+-----------+
|  6 | jenny | male |  18 | 1900-03-01 | teacher | NULL         | 30000.00 |    401 |         1 |
+----+-------+------+-----+------------+---------+--------------+----------+--------+-----------+
1 row in set (0.00 sec)