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SQL Server - Functions



What is a function in SQL Server?

In SQL Server, a function is a stored program that you can pass parameters into and return a value.

Create Function

You can create your own functions in SQL Server (Transact-SQL). Let's take a closer look.

Syntax

The syntax to create a function in SQL Server (Transact-SQL) is:
CREATE FUNCTION [schema_name.]function_name
( [ @parameter [ AS ] [type_schema_name.] datatype 
    [ = default ] [ READONLY ]
  , @parameter [ AS ] [type_schema_name.] datatype 
    [ = default ] [ READONLY ] ]
)

RETURNS return_datatype

[ WITH { ENCRYPTION
       | SCHEMABINDING
       | RETURNS NULL ON NULL INPUT
       | CALLED ON NULL INPUT
       | EXECUTE AS Clause ]

[ AS ]

BEGIN

   [declaration_section]

   executable_section

   RETURN return_value

END;
schema_name
The name of the schema that owns the function.
function_name
The name to assign to this function in SQL Server.
@parameter
One or more parameters passed into the function.
type_schema_name
The schema that owns the data type, if applicable.
datatype
The data type for @parameter.
default
The default value to assign to @parameter.
READONLY
It means that @parameter can not be overwritten by the function.
return_datatype
The datatype of the function's return value.
ENCRYPTION
It means that the source for the function will not be stored as plain text in the system views in SQL Server.
SCHEMABINDING
It means that the underlying objects can not be modified so as to affect the function.
RETURNS NULL ON NULL INPUT
It means that the function will return NULL if any parameters are NULL without having to execute the function.
CALL ON NULL INPUT
It means that the function will execute the function even if any parameters are NULL.
EXECUTE AS clause
Sets the security context to execute the function.
return_value
The value returned by the function.

Drop Function

Once you have created your function in SQL Server (Transact-SQL), you might find that you need to remove it from the database.

Syntax

The syntax to a drop a function in SQL Server (Transact-SQL) is:
DROP FUNCTION function_name;
function_name
The name of the function that you wish to drop.

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