MySQL learning notes - data type (numeric type)

Catalog

One 、 Data type refinement

1、MySQL Data types in

2、 Integer types

2.1 Type introduction

2.2 Optional attribute

2.3 Use scenarios

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2.4 How to choose

3、 Floating point type

3.1 Type introduction

3.2 Data accuracy description

4、 Fixed point number type

4.1 Type introduction

4.2 Floating point numbers VS Fixed-point number

4.3 Experience in development

5、 A type of

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One 、 Data type refinement

1、MySQL Data types in

  

2、 Integer types

2.1 Type introduction

Example ： 

8.0 There will be （）, for example tinyint(4), It represents the number of digits occupied by the plus symbol , and -128 To +127 Namely 4 position . If you use unsigned UNSIGNED, Namely 3.8.0 It is not recommended to specify the width in the future .

2.2 Optional attribute

 

1、 Do not apply ZEROFILL when , It doesn't matter whether you specify the display width or not . Use ZEROFILL when , Specify the display width as n, When insert Insufficient value for n position , Just use 0 fill , If exceeded n position , You don't have to .

2、 When using ZEROFILL when , Automatically add UNSIGNED

2.3 Use scenarios

2.4 How to choose

3、 Floating point type

3.1 Type introduction

3.2 Data accuracy description

Example ： 

1、 Use FLOAT and DOUBLE when , Better not add M and D.

2、 In programming , If floating point numbers are used , Pay special attention to the error , Because floating point numbers are inaccurate , So try to avoid using = To determine whether two floating-point numbers are equal . stay MySQL Inside , With more precise data types ：DECIMAL;

4、 Fixed point number type

4.1 Type introduction

Use DECIMAL when , General plus M and D, If not , Default (10,0).

4.2 Floating point numbers VS Fixed-point number

The advantage of floating-point number over fixed-point number is that when the length is certain , Floating point type has a wide range of values , But not exactly , It is suitable for large range of values , It can also tolerate small errors in scientific computing scenarios ( Like computational chemistry 、 Molecular modeling 、 Flow mechanics, etc )、

The value range of fixed-point number type is relatively small , But accuracy , There is no error , It is suitable for scenes that require high accuracy ( For example, scenarios involving amount calculation )

4.3 Experience in development

5、 A type of

CREATE TABLE test_bit1{

f1 BIT,f2BIT(5);  //f1 The default binary digit is 1, So only for 0 and 1,f2 Digit is 5, So you can save 0-31

}