MySQL string sorted by numeric value

1. demand

MySQL When designing a table field , Set up in order to varchar type , It is a value that is accessed , Subsequent businesses need to be sorted according to this field , Get the maximum .

According to the original sorting statement, it is ：

SELECT * FROM test_21 a ORDER BY a.testId desc;

The result is ：

This is not the desired result .

2. Method

modified

1） And int Calculate

SELECT * FROM test_21 a ORDER BY a.testId+0 desc;
SELECT * FROM test_21 a ORDER BY a.testId-2 desc;
SELECT * FROM test_21 a ORDER BY a.testId*1 desc;
SELECT * FROM test_21 a ORDER BY a.testId/4 desc;

MySQL Of varchar And int When calculating , Will be converted to int.
above 4 individual sql The results of the implementation are

2）cast() or convert()

SELECT * FROM test_21 a ORDER BY cast(a.testId as SIGNED) desc;
SELECT * FROM test_21 a ORDER BY convert(a.testId,SIGNED) desc;

These two functions are used for format conversion , There's no difference between the two ,
The grammar is ：
CAST(expr AS type)
CONVERT(expr,type)
Supported types are

value	explain
DATE	take expr convert to ’YYYY-MM-DD’ Format
DATETIME	take expr convert to ’YYYY-MM-DD HH：MM：SS’ Format
TIME	take expr convert to ’HH：MM：SS’ Format
CHAR	take expr convert to CHAR( Fixed length string ) Format
SIGNED	take expr convert to INT( Signed integers ) Format
UNSIGNED	take expr convert to INT( An unsigned integer ) Format
DECIMAL	take expr convert to FLOAT( Floating point numbers ) Format
BINARY	take expr Convert to binary format

The result is ：