数据库day03
1. 表的操作：
增：
create table 表名(
字段名 字段类型 [字段的约束],
字段名 字段类型 [字段的约束],
.......
)charset=utf8;
字段类型：
数字：
整数
tinyint
smallint
int （***************************）
mediumint
bigint
区别：
取值的范围不一样
加上unsigned， 代表只能取整数
浮点数
float
double
decimal(10,5)
如果，保存的是工资类型的话，我们推荐使用decimal
字符串类型：
char()
varchar()
区别：
1.char(4) ‘ab ’----》占4个字节,剩余的不足的字节使用空字节来补充， 身份证，
手机号， md5密码
2.varchar(4) ‘ab’ ----》 占3个字节,其中有两个字节是自己本身的大小， 还有一个
是记录字节大小的
时间日期类型：
datetime(*******************8**)
年月日 时分秒
枚举：
gender enum('male', 'female') default 'male'
列的约束 （可选的参数）：
not null :不能为null
auto_increment： 自增
primary key：主键索引 加快查询速度
default 默认值
删除：
drop table 表名;
修改：
alter table 表名 add 字段名 字段类型 [字段的约束];
alter table 表名 add 字段名 字段类型 [字段的约束] first;
alter table 表名 add 字段名 字段类型 [字段的约束] after 字段名;
alter table 表名 drop 字段名;
alter table 表名 modify 字段名 字段类型 [字段的约束] ；
alter table 表名 change 旧的字段 新的字段 字段类型 [字段的约束] ；
查：
show tables;
2. 操作数据行：
增
insert into 表名 (列1， 列2) values (值1， 值2), (值1， 值2);
删
delete from 表名；
delete from 表名 where id = 10;
delete from 表名 where id > 10;
delete from 表名 where id < 10;
delete from 表名 where id <= 10;
delete from 表名 where id >= 10;
delete from 表名 where id != 10;
delete from 表名 where id <> 10;
delete from 表名 where id = 10 and name='zekai';
truncate 表名;
改
update 表名 set name='zekai'， age=12;
update 表名 set name='zekai'， age=15 where age=12 and num=10;
查
select * from 表名;
select 列名1, 列名2,... from 表名;
select * from 表名 where id = 10;
select * from 表名 where id != 10;
select * from 表名 where id > 10;
select * from 表名 where id < 10;
select * from 表名 where id >= 10;
select * from 表名 where id <= 10;
between...and...
select * from 表名 where id between 30 and 40；
select distinct name from t66;
select * from t66 where id in (23,34,11);
今日内容：
0. null和notnull:
使用null的时候：
create table t8(
id int auto_increment primary key,
name varchar(32),
email varchar(32)
)charset=utf8;
insert into t8 (email) values ('xxxx');
mysql> insert into t8 (email) values ('xxxx');
Query OK, 1 row affected (0.05 sec)
mysql> select * from t8;
+----+------+-------+
| id | name | email |
+----+------+-------+
| 1 | NULL | xxxx |
+----+------+-------+
1 row in set (0.00 sec)
mysql> select * from t8 where name='';
Empty set (0.00 sec)
mysql> select * from t8 where name is null;
+----+------+-------+
| id | name | email |
+----+------+-------+
| 1 | NULL | xxxx |
+----+------+-------+
1 row in set (0.01 sec)
使用 notnull的时候：
create table t9(
id int auto_increment primary key,
name varchar(32) not null default '',
email varchar(32) not null default ''
)charset=utf8;
insert into t9 (email) values ('xxxx');
mysql> insert into t9 (email) values ('xxxx');
Query OK, 1 row affected (0.03 sec)
mysql> select * from t9;
+----+------+-------+
| id | name | email |
+----+------+-------+
| 1 | | xxxx |
+----+------+-------+
1 row in set (0.00 sec)
mysql> select * from t9 where name='';
+----+------+-------+
| id | name | email |
+----+------+-------+
| 1 | | xxxx |
+----+------+-------+
1 row in set (0.00 sec)
1.单表操作 (******************)
分组：
- group by
a、分组指的是：将所有记录按照某个相同字段进行归类，比如针对员工信息表的职位分组，或者按照性别
进行分组等
用法：
select 聚合函数, 选取的字段 from employee group by 分组的字段;
group by : 是分组的关键词
group by 必须和 聚合函数(count) 出现
where 条件语句和group by分组语句的先后顺序：
where > group by > having(*********)
例子：
1. 以性别为例， 进行分组， 统计一下男生和女生的人数是多少个：
select count(id), gender from employee group by gender;
+-----------+--------+
| count(id) | gender |
+-----------+--------+
| 10 | male |
| 8 | female |
+-----------+--------+
2 rows in set (0.00 sec)
mysql> select gender, count(id) as total from employee group by gender;
+--------+-------+
| gender | total |
+--------+-------+
| male | 10 |
| female | 8 |
+--------+-------+
2 rows in set (0.00 sec)
2. 对部门进行分组， 求出每个部门年龄最大的那个人？
mysql> select depart_id,max(age) from employee group by depart_id;
+-----------+----------+
| depart_id | max(age) |
+-----------+----------+
| 1 | 81 |
| 2 | 48 |
| 3 | 28 |
+-----------+----------+
3 rows in set (0.01 sec)
3. min : 求最小的
4. sum ： 求和
5. count ： 计数 数量
count 和 sum的区别：
mysql> select depart_id,count(age) from employee group by depart_id;
+-----------+------------+
| depart_id | count(age) |
+-----------+------------+
| 1 | 8 |
| 2 | 5 |
| 3 | 5 |
+-----------+------------+
3 rows in set (0.00 sec)
mysql> select depart_id,sum(age) from employee group by depart_id;
+-----------+----------+
| depart_id | sum(age) |
+-----------+----------+
| 1 | 362 |
| 2 | 150 |
| 3 | 100 |
+-----------+----------+
3 rows in set (0.03 sec)
6. avg ： 平均数
- having
表示对group by 之后的数据， 进行再一次的二次筛选
mysql> select depart_id,avg(age) from employee group by depart_id ;
+-----------+----------+
| depart_id | avg(age) |
+-----------+----------+
| 1 | 45.2500 |
| 2 | 30.0000 |
| 3 | 20.0000 |
+-----------+----------+
3 rows in set (0.00 sec)
mysql> select depart_id,avg(age) from employee group by depart_id having avg(age) > 35;
+-----------+----------+
| depart_id | avg(age) |
+-----------+----------+
| 1 | 45.2500 |
+-----------+----------+
1 row in set (0.00 sec)
mysql> select depart_id,avg(age) as pj from employee group by depart_id having pj > 35;
+-----------+---------+
| depart_id | pj |
+-----------+---------+
| 1 | 45.2500 |
+-----------+---------+
1 row in set (0.00 sec)
where 条件语句和groupby分组语句的先后顺序：
where > group by > having(*********)
升序 降序
order by
order by 字段名 asc （升序） desc(降序)
如果对多个字段进行排序，
比如：
age desc, id asc;
表示： 先对age进行降序， 如果age有相同的行， 则对id进行升序
select * from employee order by age desc, id desc;
+----+------------+--------+-----+------------+----------------------------+--------------
+------------+--------+-----------+
| id | name | gender | age | hire_date | post | post_comment |
salary | office | depart_id |
+----+------------+--------+-----+------------+----------------------------+--------------
+------------+--------+-----------+
| 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL |
8300.00 | 401 | 1 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL |
1000000.31 | 401 | 1 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL |
3500.00 | 401 | 1 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL |
3000.13 | 402 | 2 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL |
10000.00 | 401 | 1 |
| 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL |
2000.35 | 402 | 2 |
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL |
10000.13 | 403 | 3 |
| 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL |
4000.33 | 402 | 2 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL |
2100.00 | 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 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL |
3000.29 | 402 | 2 |
| 11 | 丁丁 | female | 18 | 2011-03-12 | sale | NULL |
1000.37 | 402 | 2 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL |
30000.00 | 401 | 1 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL |
9000.00 | 401 | 1 |
| 1 | egon | male | 18 | 2017-03-01 | 老男孩驻沙河办事处外交大使 | NULL |
7300.33 | 401 | 1 |
+----+------------+--------+-----+------------+----------------------------+--------------
+------------+--------+-----------+
limit
分页
limit offset， size
offset： 行数据索引,按照下表索引开始取值
size: 取多少条数据
mysql> select * from employee limit 0,10;
+----+------------+--------+-----+------------+----------------------------+--------------
+------------+--------+-----------+
| id | name | gender | age | hire_date | post | post_comment |
salary | office | depart_id |
+----+------------+--------+-----+------------+----------------------------+--------------
+------------+--------+-----------+
| 1 | egon | male | 18 | 2017-03-01 | 老男孩驻沙河办事处外交大使 | NULL |
7300.33 | 401 | 1 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL |
1000000.31 | 401 | 1 |
| 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL |
8300.00 | 401 | 1 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL |
3500.00 | 401 | 1 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL |
2100.00 | 401 | 1 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL |
9000.00 | 401 | 1 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL |
30000.00 | 401 | 1 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL |
10000.00 | 401 | 1 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL |
3000.13 | 402 | 2 |
| 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL |
2000.35 | 402 | 2 |
+----+------------+--------+-----+------------+----------------------------+--------------
+------------+--------+-----------+
10 rows in set (0.00 sec)
在取值的过程中，如果不够10条数据，那么会显示剩下的所有，所以只能显示到11--18的值。
mysql> select * from employee limit 10,10;
+----+--------+--------+-----+------------+-----------+--------------+----------+--------
+-----------+
| id | name | gender | age | hire_date | post | post_comment | salary | office |
depart_id |
+----+--------+--------+-----+------------+-----------+--------------+----------+--------
+-----------+
| 11 | 丁丁 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 |
2 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 |
2 |
| 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 |
2 |
| 14 | 张野 | 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 |
+----+--------+--------+-----+------------+-----------+--------------+----------+--------
+-----------+
8 rows in set (0.00 sec)
总结：（***************************）
使用的顺序：
select * from 表名 where 条件 group by 条件 having 条件 order by 条件 limit 条件;
条件查询的优先级别排列：
where > group by > having > order by > limit
2. 多表操作 (**************************)
外键
使用的原因：
a. 减少占用的空间
b. 只需要修改department表中一次， 其余的表中的数据就会相应的修改
一对多：
使用方法：
constraint 外键名 foreign key (被约束的字段) references 约束的表(约束的字段)
create table department(
id int auto_increment primary key,
name varchar(32) not null default ''
)charset utf8;
insert into department (name) values ('研发部');
insert into department (name) values ('运维部');
insert into department (name) values ('前台部');
insert into department (name) values ('小卖部');
create table userinfo (
id int auto_increment primary key,
name varchar(32) not null default '',
depart_id int not null default 1,
constraint fk_user_depart foreign key (depart_id) references department(id)
#constraint fk_user_depart foreign key (depart_id) references department(id),
#constraint fk_user_depart foreign key (depart_id) references department(id),
)charset utf8;
insert into userinfo (name, depart_id) values ('zekai', 1);
insert into userinfo (name, depart_id) values ('xxx', 2);
insert into userinfo (name, depart_id) values ('zekai1', 3);
insert into userinfo (name, depart_id) values ('zekai2', 4);
insert into userinfo (name, depart_id) values ('zekai3', 1);
insert into userinfo (name, depart_id) values ('zekai4', 2);
多对多：
create table boy (
id int auto_increment primary key,
bname varchar(32) not null default ''
)charset utf8;
insert into boy (bname) values ('zhangsan'),('lisi'),('zhaoliu');
create table girl (
id int auto_increment primary key,
gname varchar(32) not null default ''
)charset utf8;
insert into girl (gname) values ('cuihua'),('gangdan'),('jianguo');
create table boy2girl (
id int auto_increment primary key,
bid int not null default 1,
gid int not null default 1,
constraint fk_boy2girl_boy foreign key (bid) references boy(id),
constraint fk_boy2girl_girl foreign key (gid) references girl(id)
)charset utf8;
insert into boy2girl (bid, gid) values (1,1),(1,2),(2,3),(3,3),(2,2);
select * from boy left join boy2girl on boy.id = boy2girl.bid
mysql>select * from priv left join user on priv.uid=user.id;
+----+--------+-----+------+----------+
| id | salary | uid | id | name |
+----+--------+-----+------+----------+
| 1 | 2000 | 1 | 1 | zhangsan |
| 2 | 2800 | 2 | 2 | zekai |
| 3 | 3000 | 3 | 3 | kkk |
+----+--------+-----+------+----------+
3 rows in set (0.00 sec)
select * from boy left join boy2girl on boy.id = boy2girl.bid left join girl on
girl.id=boy2girl.gid;
mysql> select * from boy left join boy2girl on boy.id = boy2girl.bid left join girl on
girl.id=boy2girl.gid;
+----+----------+------+------+------+------+---------+
| id | bname | id | bid | gid | id | gname |
+----+----------+------+------+------+------+---------+
| 1 | zhangsan | 1 | 1 | 1 | 1 | cuihua |
| 1 | zhangsan | 2 | 1 | 2 | 2 | gangdan |
| 2 | lisi | 5 | 2 | 2 | 2 | gangdan |
| 2 | lisi | 3 | 2 | 3 | 3 | jianguo |
| 3 | zhaoliu | 4 | 3 | 3 | 3 | jianguo |
+----+----------+------+------+------+------+---------+
5 rows in set (0.00 sec)
mysql> select bname, gname from boy left join boy2girl on boy.id = boy2girl.bid left join
girl on girl.id=boy2girl.gid;
+----------+---------+
| bname | gname |
+----------+---------+
| zhangsan | cuihua |
| zhangsan | gangdan |
| lisi | gangdan |
| lisi | jianguo |
| zhaoliu | jianguo |
+----------+---------+
5 rows in set (0.00 sec)
mysql> select bname, gname from boy left join boy2girl on boy.id = boy2girl.bid left join
girl on girl.id=boy2girl.gid where bname='zhangsan';
+----------+---------+
| bname | gname |
+----------+---------+
| zhangsan | cuihua |
| zhangsan | gangdan |
+----------+---------+
2 rows in set (0.02 sec)
一对一：
user :
id name age
1 zekai 18
2 zhangsan 23
3 xxxx 19
由于salary是比较敏感的字段，因此我们需要将此字段单独拆出来， 变成一张独立的表
private：
id salary uid (外键 + unique)
1 5000 1
2 6000 2
3 3000 3
create table user (
id int auto_increment primary key,
name varchar(32) not null default ''
)charset=utf8;
insert into user (name) values ('zhangsan'),('zekai'),('kkk');
create table priv(
id int auto_increment primary key,
salary int not null default 0,
uid int not null default 1,
constraint fk_priv_user foreign key (uid) references user(id),
unique(uid)
)charset=utf8;
insert into priv (salary, uid) values (2000, 1);
insert into priv (salary, uid) values (2800, 2);
insert into priv (salary, uid) values (3000, 3);
insert into priv (salary, uid) values (6000, 1);
ERROR 1062 (23000): Duplicate entry '1' for key 'uid'
多表联查：
mysql> select * from department;
+----+--------+
| id | name |
+----+--------+
| 1 | 研发部 |
| 2 | 运维部 |
| 3 | 前台部 |
| 4 | 小卖部 |
+----+--------+
4 rows in set (0.07 sec)
mysql> select * from userinfo;
+----+--------+-----------+
| id | name | depart_id |
+----+--------+-----------+
| 1 | zekai | 1 |
| 2 | xxx | 2 |
| 3 | zekai1 | 3 |
| 4 | zekai2 | 4 |
| 5 | zekai3 | 1 |
| 6 | zekai4 | 2 |
+----+--------+-----------+
6 rows in set (0.00 sec)
left join .... on这个是左连接查询的SQL命令语法格式。
select * from userinfo left join department on userinfo.depart_id = department.id
mysql> select name from userinfo left join department on depart_id = department.id;
ERROR 1052 (23000): Column 'name' in field list is ambiguous
mysql> select userinfo.name as uname, department.name as dname from userinfo left join
department on depart_id = department.id;
+--------+--------+
| uname | dname |
+--------+--------+
| zekai | 研发部 |
| zekai3 | 研发部 |
| xxx | 运维部 |
| zekai4 | 运维部 |
| zekai1 | 前台部 |
| zekai2 | 小卖部 |
+--------+--------+
6 rows in set (0.00 sec)
right join ... on这个是右连接查询的SQL命令语法格式。
mysql> insert into department (name) values ('财务部');
Query OK, 1 row affected (0.04 sec)
mysql>
mysql> select * from department; );
+----+--------+
| id | name |
+----+--------+
| 1 | 研发部 |
| 2 | 运维部 |
| 3 | 前台部 |
| 4 | 小卖部 |
| 5 | 财务部 |
+----+--------+
5 rows in set (0.00 sec)
mysql> select * from userinfo;
+----+--------+-----------+
| id | name | depart_id |
+----+--------+-----------+
| 1 | zekai | 1 |
| 2 | xxx | 2 |
| 3 | zekai1 | 3 |
| 4 | zekai2 | 4 |
| 5 | zekai3 | 1 |
| 6 | zekai4 | 2 |
+----+--------+-----------+
6 rows in set (0.00 sec)
mysql> select userinfo.name as uname, department.name as dname from userinfo left join
department on depart_id = department.id;
+--------+--------+
| uname | dname |
+--------+--------+
| zekai | 研发部 |
| zekai3 | 研发部 |
| xxx | 运维部 |
| zekai4 | 运维部 |
| zekai1 | 前台部 |
| zekai2 | 小卖部 |
+--------+--------+
6 rows in set (0.00 sec)
mysql> select userinfo.name as uname, department.name as dname from userinfo right join
department on depart_id = department.id;
+--------+--------+
| uname | dname |
+--------+--------+
| zekai | 研发部 |
| zekai3 | 研发部 |
| xxx | 运维部 |
| zekai4 | 运维部 |
| zekai1 | 前台部 |
| zekai2 | 小卖部 |
| NULL | 财务部 |
+--------+--------+
7 rows in set (0.00 sec)
inner join.....on查询
mysql> select * from department inner join userinfo on department.id=userinfo.depart_id;
+----+--------+----+--------+-----------+
| id | name | id | name | depart_id |
+----+--------+----+--------+-----------+
| 1 | 研发部 | 1 | zekai | 1 |
| 1 | 研发部 | 5 | zekai3 | 1 |
| 2 | 运维部 | 2 | xxx | 2 |
| 2 | 运维部 | 6 | zekai4 | 2 |
| 3 | 前台部 | 3 | zekai1 | 3 |
| 4 | 小卖部 | 4 | zekai2 | 4 |
+----+--------+----+--------+-----------+
6 rows in set (0.00 sec)