How to choose the appropriate data type for fields in MySQL?

In the previous two articles, we introduced many data types , Do you have eyelashes , We are ​​mysql​​ When creating a data table in , Which data type should I choose ？ This time, let's simply sort it out .

Rules

No matter how we create the data table , First of all, we need a rule , What criteria ？

That is to say , We want to ensure that the most accurate type should be used in any case , That is, in all types that can represent the value of the column , This type uses the least storage .

Integers and floating point numbers

If you don't need a fraction , Use integers to store data ; If necessary, the decimal part , Just use the floating point number type .

For floating-point data columns , The stored values will round the decimal places defined in the column .

What do you mean ？ Come on , for instance ：

Suppose the range of values of a column is 1~99999, If you use integers , be ​​MEDIUMINT UNSIGNED​​​ It's the best type ; If you need to store decimals , Then we should use ​​float​​ Type .

Floating point types include ​​float​​​ and ​​DOUBLE​​​ type .​​DOUBLE​​​ The type accuracy is better than ​​FLOAT​​​ Type high , So , When high storage accuracy is required, you should choose ​​DOUBLE​​ type .

Floating point and fixed point numbers

Floating point numbers ​​FLOAT​​​、​​DOUBLE​​​ Relative to the fixed number ​​DECIMAL​​ What are the advantages ？

The advantage is ：

In the case of a certain length , Floating point numbers can represent a larger range of data .

Because floating point numbers are prone to error , Therefore, when the accuracy requirements are high , Fixed point number is recommended ​​DECIMAL​​ To store .

​​DECIMAL​​​ stay ​​mysql​​ Is stored as a string , It is used to define data with high accuracy requirements such as currency .

Date and time type

​​mysql​​​ There are many data types for different kinds of dates and times , such as ​​year​​​ and ​​time​​​. If you only need to record the year , Then use ​​year​​​ The type is enough ; If you only need to record the time , Then use ​​time​​ The type is enough .

If you need to record the date and time at the same time , Then we can use ​​timestamp​​​ perhaps ​​datetime​​​ type . because ​​timestamp​​​ The value range of column is less than ​​datetime​​​ Value range of . Therefore, it is best to use the date with a large storage range ​​datetime​​ type .

CHAR and VARCHAR Between the characteristics and choices

​​char​​​ and ​​varchar​​ The difference is as follows ：

• ​​char​​​ It's a fixed length character ;​​varchar​​ It's a variable length character
• ​​char​​​ The trailing space of the inserted data will be deleted automatically ,​​carchar​​ Does not remove trailing spaces

​​char​​​ It's a fixed length , So his processing speed is faster than ​​varchar​​​ It's faster , But the opposite also has disadvantages , That is a waste of storage space , So more storage is not enough , But it can be used if there are requirements on speed ​​char​​​ type , Instead, you can use ​​varchar​​ Type to implement .

ENUM and SET

​​ENUM​​ Only single value can be taken , His data list is an enumerated collection . His list of legal values allows at most 65535 Members .

therefore , When you need to select one from multiple values , have access to ​​ENUM​​.

such as , The gender field is suitable to be defined as ​​ENUM​​ type , It's only from “ male ” perhaps “ Woman ” Take a value from ;

​​SET​​ You can take multiple values . His legal value can be at most 64 Members .

An empty string is also a legal ​​SET​​​ value . When you need to take multiple values , Suitable for use ​​set​​​ type , For example, if you want to store one's hobbies, you can use ​​SET​​ type , For example, one can enjoy playing basketball , You can also like reading books .

BLOB and TEXT

​​BLOB​​​ It's a binary string ,​​TEXT​​​ It's a non binary string , Both can store large amounts of information .​​BLOB​​​ It mainly stores pictures 、 Audio information, etc , and ​​TEXT​​ Only text files can be saved .

In this case , For example, it is a multimedia platform , We're going to use ​​BLOB​​​ type , Otherwise, use ​​TEXT​​ The type is enough .

thus , In this paper, the end . 

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