How to convert varchar in mysql

Mysql method of converting varchar: 1. Use the cast function to convert; 2. Use the "select -(-field name) from table name;" method to convert; 3. Use "select field name 0 from table name;" "Mode conversion.

The operating environment of this article: windows7 system, mysql5.5 version, Dell G3 computer.

How to convert varchar in mysql?

MySQL varchar type conversion:

Question : Making a data filtering module, due to some problems with the original table design, the fields in the table are strings, and the filtering conditions are numerical values, so there is no way to compare.

Thinking: You can extract the numbers in the mysql field string and then compare them

Solution: Check the data and find three methods

1. Use the cast function

For example: SELECT CAST (field name AS UNSIGNED) FROM table name;

The cast function syntax rule is: Cast (Field name as converted type), where the type can be:

CHAR[(N)] 代表：字符型 
 DATE 代表：日期型
 DATETIME 代表：日期和时间型
 DECIMAL 代表：float型
 SIGNED 代表：int
 TIME 代表：时间型

For a string starting with a number, the result of converting it to a number is to intercept the previous number part, but the beginning part cannot For a string of numbers that is intercepted, the conversion result is 0. This needs to be noted.

2. Use -(-field name)

For example: select -(-field name) from table name;

This is more powerful, Simple and crude

3. Use the field name directly 0,

For example: select field name 0 from table name;

This is only used for field content They are all varchar type numbers and cannot contain Chinese or other characters, otherwise an error will be reported. It is generally recommended to use 1,2.

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