DbSchema | SQL Server - How to Create User-Defined Functions (UDFs)?

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SQL Server • 11-Jul-2023

by Malik Umair Sajjad

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SQL Server: How to Create User-Defined Functions in sqlcmd and DbSchema

Table of Contents

1. Introduction
2. Prerequisites
3. What is a User-Defined Function?
4. Purpose of Using User-Defined Functions
5. Restrictions and Permissions Required
6. Advantages and Limitations
7. Types of User-Defined Functions
8. Creating User-Defined Functions
   • In sqlcmd
   • In DbSchema
9. Conclusion
10. References

Introduction

This comprehensive guide will delve into the process of creating user-defined functions in SQL Server using two methods: sqlcmd and DbSchema. We will cover what user-defined functions are, their purpose, the types of user-defined functions, and their advantages and limitations. By the end of this article, you’ll be able to create and utilize your own user-defined functions effectively.

Prerequisites

Before proceeding, ensure you have:

• SQL Server installed
• Basic knowledge of SQL Server operations
• sqlcmd utility and DbSchema tool installed

For installation and establishing connection you can read our article SQL Server-How to create a database?

What is a User-Defined Function?

A User-Defined Function (UDF) is a function provided by the user of a program or an environment, in a context where the usual assumption is that functions are built into the program or environment. In SQL Server, UDFs allow you to define your own T-SQL functions that can accept 0 or more parameters and return a single scalar data value or a table data type.

Purpose of Using User-Defined Functions

User-Defined Functions serve a variety of purposes:

1. Code reuse and simplification: User-defined functions encapsulate frequently performed logic that can be reused in multiple SQL statements.
2. Expression simplification: Complex expressions can be encapsulated within a function to simplify SQL queries.
3. Additional abstraction: UDFs provide an additional level of abstraction, hiding details of complex calculations or operations.

Restrictions and Permissions Required

There are certain permissions and restrictions to keep in mind:

• The user must have CREATE FUNCTION permission in the first place.
• EXECUTE permission defaults to public. If the function specifies a user-defined type, EXECUTE permission defaults to the owner of the type.
• ALTER FUNCTION permission is required to alter the function. The new code and the old must have the same owner.

Advantages and Limitations

Advantages

1. Encapsulation: Hide complex logic under simple function calls.
2. Re-usability: Complex code can be written once and reused.
3. Maintainability: Isolate changes to complex logic.

Limitations

1. Performance overhead: UDFs add a slight overhead compared to inlined SQL.
2. Transactional limitations: You cannot use a UDF to modify database state.

Types of User-Defined Functions

There are three types of UDFs in SQL Server:

Type	_Description_
Scalar Functions	Return a single data value of the type defined in the return clause.
Table-Valued Functions	Return a table data type.
System Functions	Provided by SQL Server and return information about the SQL Server environment.

Creating User-Defined Functions

The general syntax for creating UDF is as follows:

CREATE FUNCTION [schema_name.]function_name 
( [ { @parameter_name [ type_schema_name. ] parameter_type 
    [ = default ] [READONLY] } 
    [ ,...n ]
  ]
)
RETURNS return_data_type
    [ WITH <function_option> [ ,...n ] ]
    [ AS ]
    BEGIN 
        function_body 
        RETURN scalar_expression
    END
[ ; ]

In sqlcmd

Here is an example of creating a simple scalar function in sqlcmd:

1. Open command prompt and type sqlcmd.

   sqlcmd

2. Log in to your SQL Server instance.

sqlcmd -S <server_name> -U <username> -P <password>

````
**Replace** `<server_name>`, `<username>`, and `<password>` with your specific server details and login credentials.


3. Type the following command to create a new function:

```sql
CREATE FUNCTION dbo.AddNumbers
(@Num1 INT, @Num2 INT)
RETURNS INT
AS
BEGIN
    RETURN @Num1 + @Num2;
END;
GO

This code creates a scalar User-Defined Function (UDF) named AddNumbers in SQL Server.

The AddNumbers function is a SQL Server User-Defined Function (UDF) that accepts two integer parameters, adds them together, and returns the sum. It’s a reusable piece of SQL logic that can be invoked in multiple SQL statements.

4. You can now use this function in your SQL queries as shown below:

SELECT dbo.AddNumbers(5, 10);

The above query will return 15.

This SQL statement is calling the user-defined function AddNumbers, passing in 5 and 10 as arguments, and it will return the sum of these two numbers, which is 15.

In DbSchema

Creating UDFs in DbSchema is a little bit different but still straightforward:

1. Open DbSchema and connect to your SQL Server instance.
2. Navigate to Schema > Create > Function.
3. A new dialog will open where you can enter your function definition.

CREATE FUNCTION dbo.AddNumbers
(@Num1 INT, @Num2 INT)
RETURNS INT
AS
BEGIN
    RETURN @Num1 + @Num2;
END;

4. Click Save and your new function will be created.
5. You can use this function in your SQL queries just as you would in sqlcmd.

Conclusion

In this article, we’ve introduced user-defined functions, their purpose, types, advantages, and limitations. We’ve also provided a comprehensive guide on creating UDFs in SQL Server via sqlcmd and DbSchema. With this knowledge, you can now write more reusable and maintainable SQL code.

References

1. SQL Server User-Defined Functions
2. CREATE FUNCTION (Transact-SQL)
3. DbSchema Documentation
4. sqlcmd Utility