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Usage and difference between cast and convert in SQL

高洛峰
Release: 2016-12-14 13:23:40
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1. Grammar:

1. Use CAST


CAST (expression AS data_type)


2. Use CONVERT

CONVERT (data_type[(length)], expression [, style])


3. Parameters Description


 expression

  is any valid expression.

 data_type:

 The data type provided by the target system, including bigint and sql_variant. User-defined data types cannot be used.

 length

  Optional parameter of nchar, nvarchar, char, varchar, binary or varbinary data type.

 style

 A date formatting style, which converts datetime or smalldatetime data to character data (nchar, nvarchar, char, varchar, nchar, or nvarchar data types); or a string formatting style, which converts float, real, money, or smallmoney Data is converted to character data (nchar, nvarchar, char, varchar, nchar, or nvarchar data types).

2. Code examples of cast and convert

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
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3. Style parameter description of convert function

1. Date and Time styles

Usage and difference between cast and convert in SQL

2. Float and real styles

Usage and difference between cast and convert in SQL

3. money and smallmoney style

Usage and difference between cast and convert in SQL

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