Difference Between Stored Procedure and Function in SQL Server

In this article, I am going to explain the concept of Stored Procedure and Function in SQL Server. This detailed blog will cover the following topics as follows

Introduction
What is the Stored Procedure in the SQL Server?
- Key Points
- Benefits of using Stored Procedures
- Types of Stored Procedures
What is the Function in SQL Server?
- Key Points
- Benefits of using Functions
- Types of Functions
Difference between Stored Procedure and Function In SQL Server
Conclusion

Stored Procedure in SQL Server

As per Microsoft, "A stored procedure in SQL Server is a group of one or more Transact-SQL statements or a reference to a Microsoft .NET Framework common runtime language (CLR) method".

Key Points

Stored procedures should have a name prefixed with usp_ (user-stored procedure) to distinguish them from system-stored procedures, although this is not mandatory.
A stored procedure can have both input and output parameters.
Stored procedures can use TRY...CATCH blocks for error handling.
It is executed using the EXEC or EXECUTE statement.

Benefits of using Stored Procedures

Reuse of Code
Precompiled Execution
Reduced server/client network traffic
Enhanced security controls
Easier maintenance
Improved performance

Types of Stored Procedures

This section describes the types of stored procedures in SQL Server.

User-Defined: A user-defined procedure can be created in a user-defined database or all system databases using Transact-SQL or a reference to a Microsoft.NET Framework common runtime language method.
Temporary: Temporary procedures are a form of user-defined procedures stored in tempdb, can be local or global, and have different names, visibility, and availability, similar to permanent procedures.
System: System procedures are physically stored in internal hidden resource databases and logically appear in the sys schema of all system-defined and user-defined databases. They also exist in the msdb database for scheduling alerts and jobs. Avoid using the prefix sp_ when naming user-defined procedures.

Functions in SQL Server

As per Microsoft, "Like functions in programming languages, SQL Server user-defined functions are routines that accept parameters, perform an action, such as a complex calculation, and return the result of that action as a value. The return value can either be a single scalar value or a result set".

Key Points

Functions must have a name, which cannot start with any special characters.
The function can only be used within a SELECT, WHERE, or JOIN clause.
Functions can only return a single value or a table.
Functions only accept input parameters.
Functions can't use a TRY...CATCH block for error handling.

Benefits of using Functions in SQL Server

Modular programming: User-defined functions can be created once, stored in a database, called multiple times in a program, and can be modified independently of the program source code.
Faster execution: Transact-SQL user-defined functions reduce compilation costs by caching plans and reusing them for repeated execution, resulting in faster execution times and reduced need for repairs and optimizations with each use.
Reduce network traffic: A function can be used to filter data based on complex constraints, which cannot be expressed in a single scalar expression and can be applied in the WHERE clause.

Types of Functions

This section describes the types of Functions in SQL Server.

Scalar functions: User-defined scalar functions return a single data value of the type specified in the RETURNS clause. The return type can be any data type except text, ntext, picture, cursor, and timestamp.
Table-valued functions: User-defined table-valued functions (TVFs) return a table data type.
System functions: SQL Server offers numerous system functions for performing various operations, but they cannot be modified.

Stored Procedure VS Function in SQL Server

The Stored Procedure and Function are often confusing for beginners and experienced alike, but they serve different purposes. Now, let's look at the quick difference between Stored Procedure and Function in SQL Server.

S. No.	Key Points	Stored Procedure	Function
1	Objective	Stored procedures are used to perform tasks such as modifying data or executing complex business logic. They can perform a variety of SQL operations, including calling other stored procedures or functions.	Functions are used to compute and return a single value or a table.
2	Return Values	A stored procedure can use output parameters to return data in addition to returning zero, one, or more result sets.	Functions can only return a single value or a table. Table-valued functions return a table, while scalar functions return a single value.
3	Syntax and Execution	Execute using the EXEC or EXECUTE statement.	Execute as part of the query and can be used within the SELECT, WHERE, or JOIN clause.
4	Temp Table vs Table Variable	A stored procedure can contain both temporary tables and table variables.	Only table variables can be used within a function.
5	Transaction Control	Stored procedures can contain transaction control statements. (BEGIN TRANSACTION, COMMIT, ROLLBACK)	Functions can't contain transaction control commands.
6	Error Handling.	Stored Procedure uses TRY...CATCH block for error handling.	Functions can't use TRY...CATCH block for error handling. It has limited error-handling capabilities.
7	Performance	Performance may vary depending on complexity and execution plan.	Less efficient in some cases.
8	Drawback	Modifying the database state (for example, changing data or structure) can be one of its drawbacks.	There seems to be no shortcoming in this.

EXEC dbo.StoredProcedureName 
    @Param1 = 'Value';

SELECT dbo.FunctionName(@Param1);

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Reference: https://learn.microsoft.com

Conclusion

In this blog, we have discussed the difference between Stored Procedure and Function in SQL Server.

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