mysql - 嵌套 CAST 不起作用

Question

为什么嵌套转换在 MySQL 中不起作用？ (它使用 SQL Server)

select cast(cast(myColumn as decimal(5,2)) as int) from myTable 

SQLFiddle Example

Answer 1

根据 the manual :

CAST(expr AS type) [...]

CONVERT(expr,type) [...]

The type can be one of the following values:

• BINARY[(N)]

• CHAR[(N)]

• DATE

• DATETIME

• DECIMAL[(M[,D])]

• SIGNED [INTEGER]

• TIME

• UNSIGNED [INTEGER]

所以，只要按照手册:

SELECT CAST(CAST(myColumn AS DECIMAL(5,2)) AS SIGNED) FROM myTable

或

SELECT CAST(CAST(myColumn AS DECIMAL(5,2)) AS UNSIGNED) FROM myTable