Nested CAST not working

问题

Why is a nested cast NOT working in MySQL? (It does using SQL Server)

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

SQLFiddle Example

回答1:

According to 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]

So, just follow the manual:

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

or

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

回答2:

This query is working on the concept of nested cast.

cast(sum(cast(Column_name int )+ cast(Column_name as int)) as bigint) as payment from table_name

来源：https://stackoverflow.com/questions/10347624/nested-cast-not-working