Database: Common data types

---

1. Common data types

1、数值型：
         整型
         小数：
               定点数
               浮点型
2、字符型：
         较短的文本：char、varchar
         较长的文本：text、blob（较长的二进制数据）
3、日期型

1. Numerical

(1) Integer

Integer type	byte	range
Tinyint	1	Signed: -128~127, unsigned: 0~225
Smallint	2	Signed: -32768~32767, Unsigned: 0~65535
Mediumint	3	Signed: -8388608~8388607, Unsigned: 0~1677215 (large anyway)
INT、integer	4	It's huge anyway
Bigint	8	It's huge anyway

Classification : tinyint, smallint, mediumint, int/integer, bigint (the saved return increases in order)
Features:
① The default is signed, if you want to set unsigned, you need to add the unsigned keyword

CREATE TABLE tab_int (t1 INT UNSIGNED) ;

② If the inserted value exceeds the range of the integer type, an OUT of range exception will be reported, and the critical value will be inserted;

③ If the length is not set, there will be a default length. The
length represents the maximum width of the display. If it is not enough, it will be filled with 0 on the left, but it must be used with zerofill!
For example:
INT(7) The 7 in the brackets does not refer to the range, the range is determined by the data type, but only represents the width of the displayed result

CREATE TABLE tab_int (t1 INT(7) ZEROFILL) ;#创建表
INSERT INTO tab_int VALUES(123);#插入数据
SELECT *FROM tab_int;#查看数据

Results:

(2) Decimal
classification:

1、浮点型
          FLOAT(M,D) 占4个字节
          DOUBLE(M,D) 占8个字节（精度更高）
2、定点型
          DEC(M，D)
          DECIMAL(M,D)
3、其他
          BINARY和VARBINARY用于保存较短的二进制
          ENUM用于保存枚举
          SET用于保存集合

Features:
①
M: integer part + decimal part
D: decimal part
If it exceeds the range, insert the critical value

②
Both M and D can be omitted.
If it is DECIMAL, M defaults to 10, and D defaults to 0.
If it is FLOAT and DOUBLE, the precision will be determined according to the precision of the inserted value

③The precision of fixed-point type is higher. If higher precision of inserted value is required, such as currency calculation, consider using

Principle : The simpler the selected type, the better, the smaller the type that can store the value, the better

2. Character type

1、较短的文本
          char
          varchar
2、较长的文本
          text
          blob（较大的二进制）

Short text:
Note: CHAR(M), M indicates the maximum number of characters in the value of the field

String type	Maximum number of characters	Description and storage requirements	Features	Consumption of space	effectiveness
char（M）	M (can be omitted, the default is 1)	M is an integer between 0 and 255	Fixed-length characters	Relatively expensive	high
varchar（M）	M	M is an integer between 0 and 65535	Variable length characters	Compare savings	low

3. Date type

classification:

1、date只保存日期
2、datetime保存日期+时间
3、timestamp存日期+时间（时间戳）
4、time只保存时间
5、year只保存年

Features:

Types of	byte	range	Influence of time zone, etc.
datetime	8	1000——9999	Not affected by
timestamp	4	1970-2038	Receive