前言
学习SQL语句，建表的时候，离不开的就是给字段指定数据类型
那么mysql数据库中有哪些数据类型呢？
这些数据类型的应用场景又是怎样的呢？
希望本博客对你有帮助！
数据类型
我们先从官网文档里看看有哪些数据类型
整理的数据类型如下：
数据类型还是非常多，由于篇幅有限，我会介绍前三大数据类型，数值型、日期和时间类型、字符串类型哦！
数值型
整型
数值型包括以下：
适用场景
- tinyint 1个字节，8位，常用于数值较小的数，无符号0-255，有符号-128 - 127
- smallint 2个字节，16位，无符号0-65535，有符号-32768 - 32767
- mediumint 3个字节，24位
- int 4个字节，32位
- bigint 8个字节，64位
TINYINT
示例：创建t2表，增加id字段，数据类型为tinyint，默认使用signed有符号数-128~127
root@chen 02:44 mysql>create table t2(id tinyint);
Query OK, 0 rows affected (0.02 sec)
root@chen 02:44 mysql>desc t2;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id | tinyint(4) | YES | | NULL | |
+-------+------------+------+-----+---------+-------+
1 row in set (0.00 sec)
root@chen 02:44 mysql>insert into t2(id) values(100);
Query OK, 1 row affected (0.00 sec)
root@chen 02:44 mysql>insert into t2(id) values(130);
ERROR 1264 (22003): Out of range value for column 'id' at row 1
root@chen 02:45 mysql>insert into t2(id) values(127);
Query OK, 1 row affected (0.00 sec)
root@chen 02:45 mysql>insert into t2(id) values(128);
ERROR 1264 (22003): Out of range value for column 'id' at row 1
示例：创建t3表，使用无符号数0~256
root@chen 02:45 mysql>create table t3(id tinyint unsigned);
Query OK, 0 rows affected (0.01 sec)
root@chen 02:47 mysql>desc t3;
+-------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------------+------+-----+---------+-------+
| id | tinyint(3) unsigned | YES | | NULL | |
+-------+---------------------+------+-----+---------+-------+
1 row in set (0.01 sec)
root@chen 02:47 mysql>insert into t3(id) values(130);
Query OK, 1 row affected (0.00 sec)
root@chen 02:48 mysql>insert into t3(id) values(300);
ERROR 1264 (22003): Out of range value for column 'id' at row 1
INT
示例：创建表t4，数据类型int，增加电话号码
root@chen 02:53 mysql>create table t4(id int);
Query OK, 0 rows affected (0.01 sec)
root@chen 02:55 mysql>insert into t4(id) values(18174458104);
ERROR 1264 (22003): Out of range value for column 'id' at row 1
默认有符号数，电话号码值过大，int不宜存放电话号码
示例：创建表t5，数据类型varchar，存电话号码
root@chen 02:55 mysql>create table t5(id varchar(20));
Query OK, 0 rows affected (0.05 sec)
root@chen 02:58 mysql>insert into t5(id) values(18174458104);
Query OK, 1 row affected (0.00 sec)
root@chen 03:00 mysql>select * from t5;
+-------------+
| id |
+-------------+
| 18174458104 |
+-------------+
1 row in set (0.00 sec)
定点型decimal
特点：数值精确
适用场景
常用于审计，算账等钱财不能出一点错的场景
示例
root@chen 03:00 mysql>create table salary(id int(5),name varchar(20),salary decimal(10,2));
Query OK, 0 rows affected (0.02 sec)
root@chen 03:16 mysql>desc salary;
+--------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------------+------+-----+---------+-------+
| id | int(5) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| salary | decimal(10,2) | YES | | NULL | |
+--------+---------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
decimal(10,2)，总共10位，整数占8位，小数占2位，如19923124.12
字符型
适用场景
适用于存放字符型数据
- char 定长字符串
- varchar 可变长字符串
- text 可存放文本数据
- blob 存放二进制文本，如图片、视频、音频
- enum 枚举，指定选项，固定选择
- set 集合，指定选项，内容只能由一个或多个组成
char和varchar的区别
char：character 固定长度字符串
varchar： variable character 可变长度字符串，存储会在最后多加一个空格。
存储区别
- char（len）括号中存储写的是字符长度，最大值为255，如果在存储的时候实际存储的字符串长度小于括号中的长度，那它在存储的时候会以空格补全位数进行存储；
- varchar（len），最大长度取值为65535，不会空格补全进行存储；
取数据区别
char在取值的时候会把存储后面的空格去掉
varchar和char类型在读取数据的时候，都会删除自动填充的空格。
存储大小区别
char类型最大可存储255个字节
varchar类型可存储65535个字节
text型
blob型
图片视频音频，一般不用blob型存储，一般只存储一个url或者是路径
enum枚举型
插入数据时，enum数据类型的字段必须从枚举选项中选择。
An is a string object with a value chosen from a list of permitted values that are enumerated explicitly in the column specification at table creation time. ENUM
root@lianxi 11:10 mysql>CREATE TABLE shirts (
-> name VARCHAR(40),
-> size ENUM('x-small', 'small', 'medium', 'large', 'x-large')
-> );
Query OK, 0 rows affected (0.01 sec)
root@lianxi 11:11 mysql>desc shirts;
+-------+----------------------------------------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------------------------------------------------+------+-----+---------+-------+
| name | varchar(40) | YES | | NULL | |
| size | enum('x-small','small','medium','large','x-large') | YES | | NULL | |
+-------+----------------------------------------------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
root@lianxi 11:11 mysql>INSERT INTO shirts (name, size) VALUES ('dress shirt','large'), ('t-shirt','medium'),
-> ('polo shirt','small');
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
root@lianxi 11:12 mysql>select * from shirts;
+-------------+--------+
| name | size |
+-------------+--------+
| dress shirt | large |
| t-shirt | medium |
| polo shirt | small |
+-------------+--------+
3 rows in set (0.00 sec)
set集合型
可以有零的字符串对象 或更多值，每个值都必须从 创建表时指定的允许值。 由多个组成的列值 集合成员由成员指定，成员之间用逗号分隔 ().
root@lianxi 11:21 mysql>CREATE TABLE myset (col SET('a', 'b', 'c', 'd'));
Query OK, 0 rows affected (0.04 sec)
root@lianxi 11:21 mysql>desc myset;
+-------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| col | set('a','b','c','d') | YES | | NULL | |
+-------+----------------------+------+-----+---------+-------+
1 row in set (0.00 sec)
root@lianxi 11:22 mysql>INSERT INTO myset (col) VALUES ('a,d'), ('d,a'), ('a,d,a'), ('a,d,d'), ('d,a,d');
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
root@lianxi 11:22 mysql>select * from myset;
+------+
| col |
+------+
| a,d |
| a,d |
| a,d |
| a,d |
| a,d |
+------+
5 rows in set (0.00 sec)
日期和时间型
适用场景
- year 年份
- time 时分秒
- datetime 年月日时分秒
- timestamp 年月日时分秒
- date 年月日
书写格式
存储空间
常用日期时间类型–timestamp型
The TIMESTAMP data type is used for values that contain both date and time parts. TIMESTAMP has a range of ‘1970-01-01 00:00:01’ UTC to ‘2038-01-19 03:14:07’ UTC.
timestamp消耗4个字节，2^32，换算成秒，从1970-01-01 00：00：01开始，正好算到2038年。
使用场景
- 员工考勤
- 生辰八字
示例
root@lianxi 11:42 mysql>create table t1(id int,name varchar(20),birth timestamp);
Query OK, 0 rows affected (0.01 sec)
root@lianxi 11:43 mysql>desc t1;
+-------+-------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+-------------------+-----------------------------+
| id | int(11) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| birth | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------+-------------+------+-----+-------------------+-----------------------------+
3 rows in set (0.00 sec)
root@lianxi 11:46 mysql>insert into t1(id,name,birth) values(1,'chenlibiao','2001-12-29 12:34:02');
Query OK, 1 row affected (0.00 sec)
root@lianxi 11:47 mysql>select * from t1;
+------+------------+---------------------+
| id | name | birth |
+------+------------+---------------------+
| 1 | chenlibiao | 2001-12-29 12:34:02 |
+------+------------+---------------------+
1 row in set (0.00 sec)
root@lianxi 11:47 mysql>insert into t1(id,name,birth) values(1,'felix',now());
Query OK, 1 row affected (0.01 sec)
root@lianxi 11:47 mysql>select * from t1;
+------+------------+---------------------+
| id | name | birth |
+------+------------+---------------------+
| 1 | chenlibiao | 2001-12-29 12:34:02 |
| 1 | felix | 2023-04-19 11:47:37 |
+------+------------+---------------------+
2 rows in set (0.00 sec)
now()函数，获取当前日期时间。
结语
由于篇幅有限，很多数据类型就不详细介绍啦
有需要的读者，可以查阅官网文档哦
官方文档
https://dev.mysql.com/doc/refman/8.0/en/