Difference Between Stored Procedure and Function in SQL

SQL is a database server with the main function of data storage and retrieving, as requested by other software applications. Besides, it also doesn’t matter as to whether it runs on the same computer or another within a particular network.

As far as the difference between stored procedures and functions are concerned, both of them are database objects containing a set of SQL statements to accomplish a task. In various ways, both these database objects are separate from one other.

Let’s dive in and discuss both the functions and stored procedures in the SQL server and also differentiate both these database objects in detail.

Functions

Just like the functions in programming languages, SQL Server Functions are kind of routines that accept parameters and perform an action (such as a complex calculation) while returning the outcome of that action as a value. As far as the return value is concerned, it can either be a single scalar value or a final result set.
Functions within SQL server are of different types, such as system function, scalar functions, user-defined functions, and also table-valued functions.
A user-defined function will allow you to define your own Transact-SQL functions with the help of the CREATE FUNCTION statement. User-Defined Functions make the most of zero or more input parameters while returning a single value. The user-defined functions bring back a single, scalar value, such as a char, int, or decimal value.
It is also worth mentioning here that a function may or may not have parameters, but return values are something that it should do. It can also be expressed alternatively that a user-defined function is a block of statements that offers you an output after being fed by an input.

Syntax of User-Defined Function in SQL

CREATE FUNCTION User_defined_function()
 RETURNS int  
 AS  
BEGIN  
    RETURN (SQL_statement)  
END

Pros of User-defined Functions

The best thing about user-defined functions is that they can increase efficiency with their capability to be used with certain clauses such as ‘where,’ ‘select’ or ‘case’ statements and which can help in filtering out data conveniently. In addition, we can also make the most of it by creating joins.
User-defined functions can also be used to promote a modular programming approach owing to the fact that they are defined and stored within a block and also invoked several times within the program. Besides, they can easily be modified separately without any meddling from the program.
A particular user-defined function may give a scalar value as an output or give us a table as a resultant outcome.
The execution is swift within functions, and the execution plans are cached that can result in quick execution and enhance efficiency.

Cons of User-defined functions in SQL Server

User-defined functions can give us only a one-row set as a resultant output.
User-defined functions can take comparatively less number of parameters, i.e. up to 1024 parameters, which is far less than stored procedures.
As far as user-defined function is concerned, it cannot use non-deterministic built-in functions. As far as non-deterministic functions are concerned, these are the ones that return distinguished outcomes every time, even if the same input is supplied. That is why we cannot use GETDATE() in user-defined functions.
Also, certain DML statements such as INSERT, UPDATE, DELETE cannot be used within the user-defined functions.

Stored Procedures

A set of SQL statements assigned a specific name and stored for usage in the upcoming days within multiple programs and tables can be defined as stored procedures. When a stored procedure is called for the first time, it is cached, and time is not wasted in continuous execution when we call it for subsequent.
While being stored in a database dictionary, stored procedures can be rightly called the reusable units that successfully encapsulate the logical statements within the SQL server.
Stored procedures can be also be defined as subroutines or techniques in various other programming languages that offer different benefits, including agility and efficiency.
Stored procedures offer maintainability, i.e. they provide one location to store tricky code, and rather than having to replicate various program steps at various locations of a database, we can easily put them within a stored procedure and subsequently call that particular stored procedure to encourage modular programming.
The stored procedure offers efficiency, and with the basic logic of being saved on the server as we can skip some network traffic. Opposite to having sent various commands from a client to a specific database, they can give the command to a stored procedure.

Syntax of Stored-Procedure in SQL

CREATE PROCEDURE Stored_procedure_name
AS
sql_statements
GO

Pros of Stored Procedures

Owing to the fact that the execution plan is cached on the server before, this can decrease the network traffic and thus increasing the efficiency of the application. In addition, if we are not using the stored procedure, we can execute more and more number of ad-hoc queries that can successfully contribute to network traffic.
Stored procedures are easily able to make the most of an execution plan. Whenever a query is issued, three things can happen i.e. inspecting the syntax of the query, collecting the query, and producing an execution plan. An execution plan may refer to the desired way with which the retrieval of a query from the database may happen. Because of the fact that the execution plan is generated in case of stored procedures already, it can be easily reused as the execution plan could be cached to the SQL server.
Just in case if there is a bug in our application, we can easily check the logic behind the stored procedure rather than being used by various applications. Besides, it is also not necessary to make changes everywhere. Therefore, we can say that the stored procedures offer better maintainability.
The best thing about stored procedures is that they can avoid SQL injection attacks. While building SQL statements dynamically through concatenating strings, it can result in SQL injection. However, this can be avoided by using stored procedures.

Cons of Stored Procedures

Versioning is yet another crucial important feature that stored procedures are unable to support conveniently. Complex stored procedures couldn’t also port to the upgraded versions easily.
Testing of the logic embedded within a stored procedure is rather complicated. Data errors couldn’t be generated until runtime.
Debugging is complex in the case of stored procedures, and the debugging abilities may vary from server to server in a relative database management system.
A need for a database administrator is essential to manage and maintain the complicated and bigger stored procedures based on the structure of the organization that incurs cost.