数据操作

一、数据类型
1、数字（默认都是有符号,宽度指的是显示宽度，与存储无关）
（1）tinyint [unsigned][zerofill] (1个字节存)
有符号：
-128~~127
无符号：
0~~255
（2） int [unsigned][zerofill] （4个字节存）
有符号：
-2147483648~~2147482647
无符号：
0~~4294967295
（3）bigint[unsigned][zerofill] （8个字节存）
有符号：
-9223372036854775808~~9223372036854775808
无符号：
0~~494967295
2、字符（宽度指的是字符个数 与存储有关）：
char ：定长(简单粗暴，不够则凑够固定长度存放起来，浪费空间，存取速度快)
varchar： 变长（精准，计算除待存放的数据长度，节省空间，存取速度慢）
3、日期
#注册时间
datatime 2017-09-06 10:39:46
#出生年月日 ，开学时间
data:2017-09-06
#聊天记录，上课时间
time:10:39:46
#出生年
year:2017

4、枚举与集合
enum枚举：规定一个范围，可有多个值，但是为该字段船只是，只能去规定范围中的一个
set集合：规定一个范围，可有多个值，但是为该字段船只是，只能去规定范围中的一个或多个

1：
整型测试

create table t1(id tinyint); 
create table t2(id int); 
create table t3(id bigint) ;

#测试

create table t4(salary float(5,2));

insert into t4 values(3.735);
insert into t4 values(3.735684);

2、char 与 varcahr测试

create table t6(name char(4));
insert into t6 values('alex')
insert into t6 values('欧德博爱')；
insert into t6 values('艾利克斯')；





create table t7(x char(5),y varchar(5));
insert into t7 values('addd','dsds') #char_length：查看字符长度
 insert into t7 values('你好啊'，'好你妹')#char_length：查看字符长度

了解
insert into t7 values('你好啊'，'好你妹')#length:查看字节长度
select char_length(x),char_length(y) from t7;

注意两点：
insert into t7 values('abc','abc');#length:查看字节长度
select * from t7 where y='abc '; #去掉末尾的空格然后去比较

3、日期

create table student(
id int ,
name char(5),
born_date date,
born_year year,
reg_time datetime,
class_time time
);
insert into student values(1,'alex',now(),now(),now(),now());
insert into student values(1,'alex','2017-09-06','2017','2017-09-06 10:09:36','09:06:36');

4、枚举与集合

create table student1(
id int  primary key auto_increment,
name char(5),
sex enum('male','female'),
hobbies set('music','read','coding')
);

insert into student1(name,sex,hobbies) values('egon','male','music,read,coding');

1 简单查询
select * from employee;
select name,salary from employee;

2 where条件
select name,salary from employee where salary > 10000;
select name,salary from employee where salary > 10000 and salary < 20000;
select name,salary from employee where salary between 10000 and 20000;
select name,salary from employee where salary not between 10000 and 20000;

select name,salary from employee where salary = 10000 or salary = 20000 or salary = 30000;
select name,salary from employee where salary in (10000,20000,30000);


select * from employee where salary = 10000 or age = 18 or sex='male';

select * from employee where post_comment is Null;
select * from employee where post_comment = Null;
select * from employee where post_comment is not Null;

select * from employee where name like '%n%';

select * from employee where name like 'e__n';

3 group by分组
mysql> select depart_id,group_concat(name)  from employee group by depart_id;
+-----------+--------------------------------------------------------------+
| depart_id | group_concat(name)                                           |
+-----------+--------------------------------------------------------------+
|         1 | egon,alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙   |
|         2 | 歪歪,丫丫,丁丁,星星,格格                                     |
|         3 | 张野,程咬金,程咬银,程咬铜,程咬铁                             |
+-----------+--------------------------------------------------------------+
3 rows in set (0.00 sec)

mysql> select depart_id,count(id)  from employee group by depart_id;
+-----------+-----------+
| depart_id | count(id) |
+-----------+-----------+
|         1 |         8 |
|         2 |         5 |
|         3 |         5 |
+-----------+-----------+
3 rows in set (0.01 sec)

mysql> select depart_id,group_concat(id)  from employee group by depart_id;
+-----------+------------------+
| depart_id | group_concat(id) |
+-----------+------------------+
|         1 | 1,2,3,4,5,6,7,8  |
|         2 | 9,10,11,12,13    |
|         3 | 14,15,16,17,18   |
+-----------+------------------+
3 rows in set (0.00 sec)

mysql> select depart_id,count(id)  from employee group by depart_id;
+-----------+-----------+
| depart_id | count(id) |
+-----------+-----------+
|         1 |         8 |
|         2 |         5 |
|         3 |         5 |
+-----------+-----------+
3 rows in set (0.00 sec)

mysql> select depart_id,max(salary) from employee group by depart_id;
+-----------+-------------+
| depart_id | max(salary) |
+-----------+-------------+
|         1 |  1000000.31 |
|         2 |     4000.33 |
|         3 |    20000.00 |
+-----------+-------------+
3 rows in set (0.00 sec)

mysql> select depart_id,min(salary) from employee group by depart_id;
+-----------+-------------+
| depart_id | min(salary) |
+-----------+-------------+
|         1 |     2100.00 |
|         2 |     1000.37 |
|         3 |    10000.13 |
+-----------+-------------+
3 rows in set (0.00 sec)

mysql> select depart_id,sum(salary) from employee group by depart_id;
+-----------+-------------+
| depart_id | sum(salary) |
+-----------+-------------+
|         1 |  1070200.64 |
|         2 |    13001.47 |
|         3 |    84000.13 |
+-----------+-------------+
3 rows in set (0.00 sec)

mysql> select depart_id,avg(salary) from employee group by depart_id;
+-----------+---------------+
| depart_id | avg(salary)   |
+-----------+---------------+
|         1 | 133775.080000 |
|         2 |   2600.294000 |
|         3 |  16800.026000 |
+-----------+---------------+
3 rows in set (0.00 sec)