Cast function in Sql Server 2012

The CAST function is used to explicitly convert an expression of one data type to another.

In many cases, a database will automatically convert one data type into another of same family(small type is converted high type vice versa is not possible)when needed.

On the other hand, there are instances when that is not the case, or when you want to explicitly specify what data type to change into. In these cases, you can use the CAST function.

Syntax of CAST Function :                 CAST ( expression AS data_type )

expression is any valid sql server expression./Column Name/direct value.

data_type is sql server data type to convert expression into that data type.i.e target data type.

Examples:

Example 1 : Use of CAST function in select clause

SELECT CAST ( 10.20 AS INT )

Output: 10
Above example converts 10.20 float value into an integer value and returns 10

Example 2 :

SELECT CAST ( 10.20 AS char(5))

Output: 10.

Above example converts 10.20 float value into an char value and returns 10.20(five characters)

NOTE: 

1.This will be used at programming level  i.e we are not changing the table structure but we are reading the data according to our requirement and using the data. In order to change the structure we have alter command is available.
2.The target datatype must capable of storing the value other wise it will throw an error

Let me know if you need more clarification on this.

Thanks

GSV