CAST和CONVERT函式將一種資料型別轉換為另一種資料型別

語法：

Syntax for CAST:
CAST ( expression AS data_type [ ( length ) ] )

Syntax for CONVERT:
CONVERT ( data_type [ ( length ) ] , expression [ , style ] )

Syntax for CAST:
CAST ( expression AS data_type [ ( length ) ] )

Syntax for CONVERT:
CONVERT ( data_type [ ( length ) ] , expression [ , style ] )
 

引數：

具體的使用示例如下：

select CAST('123' as int)   -- 123
select CONVERT(int, '123')  -- 123

select CAST(123.4 as int)   -- 123
select CONVERT(int, 123.4)  -- 123 

select CAST('123.4' as int)
select CONVERT(int, '123.4')
-- Conversion failed when converting the varchar value '123.4' to data type int.

select CAST('123.4' as decimal)  -- 123
select CONVERT(decimal, '123.4') -- 123 


select CAST('123.4' as decimal(9,2))  -- 123.40
select CONVERT(decimal(9,2), '123.4') -- 123.40


declare @Num money
set @Num = 1234.56
select CONVERT(varchar(20), @Num, 0)  -- 1234.56
select CONVERT(varchar(20), @Num, 1)  -- 1,234.56
select CONVERT(varchar(20), @Num, 2)  -- 1234.5600