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Introduction to Stored Procedures and its benefits

Imagine a situation where we have to use the same query again and again or we have a set of queries that need to run again and again at regular interval. Think of a scenario where you need to incorporate a complex logic into your query before giving out the final output. 

Standard SQL queries do not allow the user to include any conditional statements in them. They only allow users to retrieve or modify data stored inside a database.

To apply business logic or apply business logic to store data we need to first get the data, process it and update the database.

The Relational database management system allows developers to create programs to process the data in the database. These are called Stored Procedure.

For the next few pages of the blog, we will learn about stored procedures and their uses in database management.

What is Stored Procedure

Have you heard of a Fibonacci number series? A Fibonacci number series is a series where the following output of the series is the sum of the previous two outputs. The output is somewhat like this:

0
1
1
2
3
5
8
13

If you are asked to write logic to provide users an output such as above how would you do that. One easy way of doing it is to write a set of union all statements to give out the output. This is how it would look like

select 0
union all
select 1
union all
select 1
union all
select 2
union all
select 3
union all
select 5
union all
select 8
union all
select 13

The output is

Introduction to Stored Procedures and its benefits

But as you can well understand this is a hardcoded solution and not flexible. What if you were asked to extend the series to 13 rows?

This is where a stored procedure comes into play. Stored procedure is a special feature of a database management system that allows you to extend the functionality of a database by writing logical program blocks. Now let us rewrite the above code into something like below:

Create PROCEDURE Storedproc


AS
BEGIN

declare @x as int;
declare @y as int;
declare @z as int;
declare @k as int;
      set @x=0;
  set @y=1;
  set @z=1;
  print @x;
  print @y; 

while @z <> 15
Begin
    set @[email protected] + @x;

print @k;
set @[email protected];
set @[email protected];
set @[email protected]+1;
     end;

END
GO

Execute the procedure as

 exec Storedproc

The output is

Introduction to Stored Procedures and its benefits
 

As you can see just changing the loop counter, you can change the number of rows as output. This is the beauty of stored procedure.

Types of Stored Procedures

System defined stored procedure Extended Stored procedure User-defined Stored Procedure
Preloaded in the system when SQL Server is installed These are stored procedures that reside in DLLs Stored procedures developed by individual users

System defined stored procedure

Some example of system- defined stored procedure is

  1. Sp_help
  2. Sp_table
  3. Sp_depends

Sp_help

exec sp_helptext [storedproc_test]

Shows the details of a stored procedure provided as parameter

Introduction to Stored Procedures and its benefits 3

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Sp_table

Gives the details of all the tables present in a database

EXEC sys.sp_tables  

Introduction to Stored Procedures and its benefits 4

Sp_depends

Gives the dependent object details in multiple rows.

Sp_depends [SalesReason]

Extended Stored Procedure

To add an extended stored procedure to SQL Server you need to use sp_addextendedproc system stored procedure.

sp_addextendedproc 'xp_sample','xp_sample.dll'

To remove an extended stored procedure from SQL Server you need to use 

sp_dropextendedproc 'xp_sample','xp_sample.dll'

User-defined Stored Procedure

Here we try to write an SP which gives an output somewhat like below.


*
**
***
****
*****

Here is the code

create  PROCEDURE printstar

-- Add the parameters for the stored procedure here


AS
BEGIN
declare @i  int;
declare @k  int;
declare @x varchar(max);
set @i=0;
set @k=0;
print @x;
set @x='';
    while @i <= 5
begin
    while @k <= @i
begin
  set @[email protected] + '*';

  set @[email protected] +1;

end
print @x;
set @x='';
set @k=0;
set @[email protected]+1;

     end

END
GO

You execute it with the following command.

exec printstar

Introduction to Stored Procedures and its benefits 5

Here is the output

Parameterized Stored procedure

Parameterized stored procedures are Stored Procedures where you can pass on some values some outside. Let  us take a simple example of adding two numbers using a stored procedure.

The code is as below


create  PROCEDURE addtwovalue

@val1 int,
@val2 int
AS
BEGIN
declare @sumval int;
set @[email protected] + @val2;
print @sumval;
END
GO

You mention the parameters just after the name of the stored procedure. Here @val1 and @val2 are two parameters.

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You pass the parameter into the stored procedure as below

exec addtwovalue 1,2

The output is as below

Introduction to Stored Procedures and its benefits 6

Stored procedure for insert

Stored procedure can be used for the insert operation.

Let us first create a test table and use it to insert a row with parameters.

create table testtab

(


   name varchar(50),

   address varchar(50)

  )

 


Now let us create a stored procedure to insert a record into the table.


CREATE PROCEDURE sp_inst
@name varchar(50),
@address varchar(50)
AS
BEGIN
insert into testtab values(@name,@address);

END
GO

To execute the stored procedure

exec sp_inst 'Testname','Testaddr'

Here is the final output

estname','Testaddr

Stored procedure for update

Let us take the same table  testtab for the update example.

The code for stored procedure for the update will be as follows.


create PROCEDURE sp_upd
@name varchar(50),
@address varchar(50)
AS
BEGIN
update testtab set [email protected] where [email protected]

END
GO

To run the Procedure we need

exec sp_upd 'Testname','Testaddr1'

The out put is

Introduction to Stored Procedures and its benefits

Stored procedure for Delete

Let us take the same table testtab for the delete example.

The code for the stored procedure for delete will be as follows.


alter PROCEDURE sp_del
@name varchar(50)
AS
BEGIN
delete from testtab where [email protected]
END
GO

To run the procedure we need

exec sp_del 'Testname'

The output is

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Introduction to Stored Procedures and its benefits 7

Error handling in stored procedure

To catch error in a stored procedure we use Begin Try End Try and Begin Catch and End Catch block.

Here is an example code on the error handling process. The code deliberately generates a divided by zero error and catch and displays the error using the Try Catch block.


CREATE PROCEDURE usp_GetErrorInfo  

AS  

SELECT  

    ERROR_NUMBER() AS ErrorNumber 
    ,ERROR_SEVERITY() AS ErrorSeverity  
    ,ERROR_STATE() AS ErrorState  
    ,ERROR_PROCEDURE() AS ErrorProcedure  
    ,ERROR_LINE() AS ErrorLine  
    ,ERROR_MESSAGE() AS ErrorMessage;  

GO  

BEGIN TRY  

    -- Generate divide-by-zero error. 
    SELECT 1/0;  

END TRY  

BEGIN CATCH  

    -- Execute error retrieval routine.  
    EXECUTE usp_GetErrorInfo;  

END CATCH;   

The output is

Introduction to Stored Procedures and its benefits 8

Stored Procedure with Out Parameter

We have seen how to send a parameter into a stored procedure. But how would you send back a value from a stored procedure? The next paragraph deals with the out parameter of stored procedure.

Here is how the code looks like.



Create PROCEDURE dbo.uspGetAddressCount @City nvarchar(30), @AddressCount int OUTPUT

AS
BEGIN

SELECT @AddressCount = count(*) 
FROM AdventureWorks2016.Person.Address 
WHERE City = @City

 

END

 

To execute the stored procedure we need to use the following group of statements

declare @rowCount int

exec uspGetAddressCount 'Bothell', @AddressCount = @rowCount output
print @rowcount

The output will look like below
 

@rowcount

Summary

In the above write-up we have tried to give you an overview of different types of stored procedures and how they can be used. It is not a comprehensive guide but this would give the reader a sneak pick on the definition of stored procedure, their capabilities, types and how to use them.

Read: Online SQL Queries for Practice Questions with Answers

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    Sanchayan Banerjee

    I love to learn new things and also like sharing my knowledge with others. As an experienced IT Professional I like to update myself constantly with new and upcoming technologies. The database management system is one of my favorite subjects which I constantly explore.


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