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Data Type Conversion - SQL Server

 In SQL Server, data type conversion allows us to change the data type of a value from one data type to another. Data type conversion can be implicit or explicit, depending on whether the conversion is performed automatically or explicitly by the user. In this blog, we will discuss data type conversion in SQL Server with examples.

Implicit Data Type Conversion

Implicit data type conversion is the automatic conversion of data from one data type to another. SQL Server automatically converts data when it is required, such as during arithmetic operations. Here is an example of implicit data type conversion:

DECLARE @x int = 5

DECLARE @y float = 3.14

DECLARE @result float

SET @result = @x + @y

SELECT @result

In this example, we have declared two variables, @x as an integer and @y as a float. We then add the values of @x and @y and store the result in @result, which is also a float. Since the data types of @x and @y are different, SQL Server implicitly converts the value of @x to a float before performing the addition. The output of this query will be 8.14.

Explicit Data Type Conversion

Explicit data type conversion is the conversion of data from one data type to another using conversion functions. SQL Server provides a number of built-in conversion functions, including CAST and CONVERT. Here is an example of explicit data type conversion using the CAST function:

DECLARE @x varchar(10) = '123'

DECLARE @y int

SET @y = CAST(@x AS int)

SELECT @y

In this example, we have declared a variable @x as a varchar and set its value to '123'. We then convert the value of @x to an integer using the CAST function and store the result in @y. The output of this query will be 123.

Another example of explicit data type conversion using the CONVERT function:

DECLARE @x datetime = '2022-03-21 12:34:56'

DECLARE @y varchar(20)

SET @y = CONVERT(varchar(20), @x, 120)

SELECT @y

In this example, we have declared a variable @x as a datetime and set its value to '2022-03-21 12:34:56'. We then convert the value of @x to a varchar using the CONVERT function and store the result in @y. The third argument of the CONVERT function, 120, specifies the format of the output. The output of this query will be '2022-03-21 12:34:56'.

Conclusion

In SQL Server, data type conversion allows us to change the data type of a value from one data type to another. Data type conversion can be implicit or explicit, depending on whether the conversion is performed automatically or explicitly by the user. By using the appropriate conversion functions, we can ensure that our SQL Server queries and procedures are accurate, efficient, and reliable.

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