SQL Server Stored Procedure Basics & Introduction to Stored Procedure

SQL Server Stored Procedure for Beginners (Introduction)

Overview
A stored procedure is nothing more than prepared SQL code that you save so you can reuse the code over and over again.  So if you think about a query that you write over and over again, instead of having to write that query each time you would save it as a stored procedure and then just call the stored procedure to execute the SQL code that you saved as part of the stored procedure.

In addition to running the same SQL code over and over again you also have the ability to pass parameters to the stored procedure, so depending on what the need is the stored procedure can act accordingly based on the parameter values that were passed.

Take a look through each of these topics to learn how to get started with stored procedure development for SQL Server.

You can either use the outline on the left or click on the arrows to the right or below to scroll through each of these topics.

Different options for creating SQL Server stored procedures

Overview
There are various options that can be used to create stored procedures.  In these next few topics we will discuss creating a simple stored procedure to more advanced options that can be used when creating stored procedures.

Explanation
Some of the topics we will cover include:

• Creating a simple stored procedure
• Using input parameters
• Using output parameters
• Using Try Catch

Creating a simple stored procedure   (CREATE PROCEDURE)

·         Overview
As mentioned in the tutorial overview a stored procedure is nothing more than stored SQL code that you would like to use over and over again.  In this example we will look at creating a simple stored procedure.

·         Explanation
Before you create a stored procedure you need to know what your end result is, whether you are selecting data, inserting data, etc.. 

·         In this simple example we will just select all data from the Person.Address table that is stored in the AdventureWorks database.

·         So the simple T-SQL code would be as follows which will return all rows from this table.

SELECT * FROM AdventureWorks.Person.Address

·         To create a stored procedure to do this the code would look like this:

CREATE PROCEDURE uspGetAddress AS SELECT * FROM AdventureWorks.Person.Address GO

·         To call the procedure to return the contents from the table specified, the code would be:

EXEC uspGetAddress --or just simply uspGetAddress

·        

---

·         When creating a stored procedure you can either use CREATE PROCEDURE or CREATE PROC.  After the stored procedure name you need to use the keyword "AS" and then the rest is just the regular SQL code that you would normally execute.

·         On thing to note is that you cannot use the keyword "GO" in the stored procedure.  Once the SQL Server compiler sees "GO" it assumes it is the end of the batch.

·         Also, you can not change database context within the stored procedure such as using "USE dbName" the reason for this is because this would be a separate batch and a stored procedure is a collection of only one batch of statements.

How to create a SQL Server stored procedure with parameters

·         Overview
The real power of stored procedures is the ability to pass parameters and have the stored procedure handle the differing requests that are made.  In this topic we will look at passing parameter values to a stored procedure.

·         Explanation
Just like you have the ability to use parameters with your SQL code you can also setup your stored procedures to except one or more parameter values.

·         One Parameter

·         In this example we will query the Person.Address table from the AdventureWorks database, but instead of getting back all records we will limit it to just a particular city.  This example assumes there will be an exact match on the City value that is passed.

CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SELECT * FROM AdventureWorks.Person.Address WHERE City = @City GO

·         To call this stored procedure we would execute it as follows:

EXEC uspGetAddress @City = 'New York'

·         We can also do the same thing, but allow the users to give us a starting point to search the data.  Here we can change the "=" to a LIKE and use the "%" wildcard.

CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SELECT * FROM AdventureWorks.Person.Address WHERE City LIKE @City + '%' GO

·         In both of the proceeding examples it assumes that a parameter value will always be passed. If you try to execute the procedure without passing a parameter value you will get an error message such as the following:

Msg 201, Level 16, State 4, Procedure uspGetAddress, Line 0 Procedure or function 'uspGetAddress' expects parameter '@City', which was not supplied.

·         Default Parameter Values

·         In most cases it is always a good practice to pass in all parameter values, but sometimes it is not possible.  So in this example we use the NULL option to allow you to not pass in a parameter value.  If we create and run this stored procedure as is it will not return any data, because it is looking for any City values that equal NULL.

CREATE PROCEDURE uspGetAddress @City nvarchar(30) = NULL AS SELECT * FROM AdventureWorks.Person.Address WHERE City = @City GO

·         We could change this stored procedure and use the ISNULL function to get around this.  So if a value is passed it will use the value to narrow the result set and if a value is not passed it will return all records.

CREATE PROCEDURE uspGetAddress @City nvarchar(30) = NULL AS SELECT * FROM AdventureWorks.Person.Address WHERE City = ISNULL(@City,City) GO

·         Multiple Parameters

·         Setting up multiple parameters is very easy to do.  You just need to list each parameter and the data type separated by a comma as shown below.

CREATE PROCEDURE uspGetAddress @City nvarchar(30) = NULL, @AddressLine1 nvarchar(60) = NULL AS SELECT * FROM AdventureWorks.Person.Address WHERE City = ISNULL(@City,City) AND AddressLine1 LIKE '%' + ISNULL(@AddressLine1 ,AddressLine1) + '%' GO

·         To execute this you could do any of the following:

EXEC uspGetAddress @City = 'Calgary' --or EXEC uspGetAddress @City = 'Calgary', @AddressLine1 = 'A' --or EXEC uspGetAddress @AddressLine1 = 'Acardia' -- etc...
Returning stored procedure parameter values to a calling stored procedure   (OUTPUT)

Overview
In a previous topic we discussed how to pass parameters into a stored procedure, but another option is to pass parameter values back out from a stored procedure.  One option for this may be that you call another stored procedure that does not return any data, but returns parameter values to be used by the calling stored procedure.

Explanation
Setting up output paramters for a stored procedure is basically the same as setting up input parameters, the only difference is that you use the OUTPUT clause after the parameter name to specify that it should return a value.  The output clause can be specified by either using the keyword "OUTPUT" or just "OUT".

Simple Output

CREATE PROCEDURE uspGetAddressCount @City nvarchar(30), @AddressCount int OUTPUT AS SELECT @AddressCount = count(*) FROM AdventureWorks.Person.Address WHERE City = @City

Or it can be done this way:

CREATE PROCEDURE uspGetAddressCount @City nvarchar(30), @AddressCount int OUT AS SELECT @AddressCount = count(*) FROM AdventureWorks.Person.Address WHERE City = @City

To call this stored procedure we would execute it as follows.  First we are going to declare a variable, execute the stored procedure and then select the returned valued.

DECLARE @AddressCount int EXEC uspGetAddressCount @City = 'Calgary', @AddressCount = @AddressCount OUTPUT SELECT @AddressCount

This can also be done as follows, where the stored procedure parameter names are not passed.

DECLARE @AddressCount int EXEC uspGetAddressCount 'Calgary', @AddressCount OUTPUT SELECT @AddressCount
Using try catch in SQL Server stored procedures   (TRY...CATCH)

Overview
A great new option that was added in SQL Server 2005 was the ability to use the Try..Catch paradigm that exists in other development languages.  Doing error handling in SQL Server has not always been the easiest thing, so this option definitely makes it much easier to code for and handle errors.

Explanation
If you are not familiar with the Try...Catch paradigm it is basically two blocks of code with your stored procedures that lets you execute some code, this is the Try section and if there are errors they are handled in the Catch section. 

Let's take a look at an example of how this can be done.  As you can see we are using a basic SELECT statement that is contained within the TRY section, but for some reason if this fails it will run the code in the CATCH section and return the error information.

CREATE PROCEDURE uspTryCatchTest AS BEGIN TRY     SELECT 1/0 END TRY BEGIN CATCH     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; END CATCH
Using comments in a SQL Server stored procedure

Overview
One very helpful thing to do with your stored procedures is to add comments to your code.  This helps you to know what was done and why for future reference, but also helps other DBAs or developers that may need to make modifications to the code.

Explanation
SQL Server offers two types of comments in a stored procedure; line comments and block comments.   The following examples show you how to add comments using both techniques.  Comments are displayed in green in a SQL Server query window.

Line Comments

To create line comments you just use two dashes "--" in front of the code you want to comment.  You can comment out one or multiple lines with this technique.

In this example the entire line is commented out.

-- this procedure gets a list of addresses based -- on the city value that is passed CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SELECT * FROM AdventureWorks.Person.Address WHERE City = @City GO

This next example shows you how to put the comment on the same line.

-- this procedure gets a list of addresses based on the city value that is passed CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SELECT * FROM AdventureWorks.Person.Address WHERE City = @City -- the @City parameter value will narrow the search criteria GO

Block Comments

To create block comments the block is started with "/*" and ends with "*/".   Anything within that block will be a comment section.

/* -this procedure gets a list of addresses based  on the city value that is passed -this procedure is used by the HR system      */ CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SELECT * FROM AdventureWorks.Person.Address WHERE City = @City GO

Combining Line and Block Comments

You can also use both types of comments within a stored procedure.

/* -this procedure gets a list of addresses based  on the city value that is passed -this procedure is used by the HR system      */ CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SELECT * FROM AdventureWorks.Person.Address WHERE City = @City -- the @City parameter value will narrow the search criteria GO
Naming conventions for SQL Server stored procedures

Overview
One good thing to do for all of your SQL Server objects is to come up with a naming convention to use.  There are not any hard and fast rules, so this is really just a guideline on what should be done.

Explanation
SQL Server uses object names and schema names to find a particular object that it needs to work with.  This could be a table, stored procedure, function ,etc...

It is a good practice to come up with a standard naming convention for you objects including stored procedures.

---

Do not use sp_ as a prefix

One of the things you do not want to use as a standard is "sp_".  This is a standard naming convention that is used in the master database.  If you do not specify the database where the object is, SQL Server will first search the master database to see if the object exists there and then it will search the user database. So avoid using this as a naming convention.

---

Standardize on a Prefix

It is a good idea to come up with a standard prefix to use for your stored procedures.  As mentioned above do not use "sp_", so here are some other options.

• usp_
• sp
• usp
• etc...

To be honest it does not really matter what you use.  SQL Server will figure out that it is a stored procedure, but it is helpful to differentiate the objects, so it is easier to manage.

So a few examples could be:

• spInsertPerson
• uspInsertPerson
• usp_InsertPerson
• InsertPerson

Again this is totally up to you, but some standard is better than none.

---

Naming Stored Procedure Action

I liked to first give the action that the stored procedure takes and then give it a name representing the object it will affect.

So based on the actions that you may take with a stored procedure, you may use:

• Insert
• Delete
• Update
• Select
• Get
• Validate
• etc...

So here are a few examples:

• uspInsertPerson
• uspGetPerson
• spValidatePerson
• SelectPerson
• etc...

Another option is to put the object name first and the action second, this way all of the stored procedures for an object will be together.

• uspPersonInsert
• uspPersonDelete
• uspPersonGet
• etc...

Again, this does not really matter what action words that you use, but this will be helpful to classify the behavior characteristics.

---

Naming Stored Procedure Object

The last part of this is the object that you are working with.  Some of these may be real objects like tables, but others may be business processes.  Keep the names simple, but meaningful.  As your database grows and you add more and more objects you will be glad that you created some standards.

So some of these may be:

• uspInsertPerson - insert a new person record
• uspGetAccountBalance - get the balance of an account
• uspGetOrderHistory - return list of orders

---

Schema Names

Another thing to consider is the schema that you will use when saving the objects.  A schema is the a collection of objects, so basically just a container.  This is useful if you want to keep all utility like objects together or have some objects that are HR related, etc...

This logical grouping will help you differentiate the objects further and allow you to focus on a group of objects.

Here are some examples of using a schema:

• HR.uspGetPerson
• HR.uspInsertPerson
• UTIL.uspGet
• UTIL.uspGetLastBackupDate
• etc...

To create a new schema you use the CREATE SCHEMA command

Here is a simple example to create a new schema called "HR" and giving authorization to this schema to "DBO".

CREATE SCHEMA [HumanResources] AUTHORIZATION [dbo]

---

Putting It All Together

So you basically have four parts that you should consider when you come up with a naming convention:

• Schema
• Prefix
• Action
• Object

Take the time to think through what makes the most sense and try to stick to your conventions.

Reducing amount of network data for SQL Server stored procedures   (SET NOCOUNT ON)

Overview
There are many tricks that can be used when you write T-SQL code.  One of these is to reduce the amount of network data for each statement that occurs within your stored procedures.  Every time a SQL statement is executed it returns the number of rows that were affected.  By using "SET NOCOUNT ON" within your stored procedure you can shut off these messages and reduce some of the traffic.

Explanation
As mentioned above there is not really any reason to return messages about what is occuring within SQL Server when you run a stored procedure.  If you are running things from a query window, this may be useful, but most end users that run stored procedures through an application would never see these messages. 

You can still use @@ROWCOUNT to get the number of rows impacted by a SQL statement, so turning SET NOCOUNT ON will not change that behavior.

Not using SET NOCOUNT ON

Here is an example without using SET NOCOUNT ON:

-- not using SET NOCOUNT ON CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SELECT * FROM AdventureWorks.Person.Address WHERE City = @City GO

The messages that are returned would be similar to this:

(23 row(s) affected)

Using SET NOCOUNT ON

This example uses the SET NOCOUNT ON as shown below.  It is a good practice to put this at the beginning of the stored procedure.

-- using SET NOCOUNT ON CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SET NOCOUNT ON SELECT * FROM AdventureWorks.Person.Address WHERE City = @City GO

The messages that are returned would be similar to this:

Command(s) completed successfully.

Using SET NOCOUNT ON and @@ROWCOUNT

This example uses SET NOCOUNT ON, but will still return the number of rows impacted by the previous statement.  This just shows that this still works.

-- not using SET NOCOUNT ON CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SET NOCOUNT ON SELECT * FROM AdventureWorks.Person.Address WHERE City = @City PRINT @@ROWCOUNT GO

The messages that are returned would be similar to this:

23

SET NOCOUNT OFF

If you wanted to turn this behavior off, you would just use the command "SET NOCOUNT OFF".

Deleting a SQL Server stored procedure   (DROP PROCEDURE)

Overview
In addition to creating stored procedures there is also the need to delete stored procedures.  This topic shows you how you can delete stored procedures that are no longer needed.

Explanation
The syntax is very straightforward to drop a stored procedure, here are some examples.

Dropping Single Stored Procedure

To drop a single stored procedure you use the DROP PROCEDURE or DROP PROC command as follows.

DROP PROCEDURE uspGetAddress GO -- or DROP PROC uspGetAddress GO -- or DROP PROC dbo.uspGetAddress -- also specify the schema

Dropping Multiple Stored Procedures

To drop multiple stored procedures with one command you specify each procedure separated by a comma as shown below.

DROP PROCEDURE uspGetAddress, uspInsertAddress, uspDeleteAddress GO -- or DROP PROC uspGetAddress, uspInsertAddress, uspDeleteAddress GO
Modifying an existing SQL Server stored procedure   (ALTER PROCEDURE)

Overview
When you first create your stored procedures it may work as planned, but how to do you modify an existing stored procedure.  In this topic we look at the ALTER PROCEDURE command and it is used.

Explanation
Modifying or ALTERing a stored procedure is pretty simple.  Once a stored procedure has been created it is stored within one of the system tables in the database that is was created in.  When you modify a stored procedure the entry that was originally made in the system table is replaced by this new code.  Also, SQL Server will recompile the stored procedure the next time it is run, so your users are using the new logic.  The command to modify an existing stored procedure is ALTER PROCEDURE or ALTER PROC.

Modifying an Existing Stored Procedure

Let's say we have the following existing stored procedure:  This allows us to do an exact match on the City.

CREATE PROCEDURE uspGetAddress @City nvarchar(30) AS SELECT * FROM AdventureWorks.Person.Address WHERE City = @City GO

Let's say we want to change this to do a LIKE instead of an equals.

To change the stored procedure and save the updated code you would use the ALTER PROCEDURE command as follows.

ALTER PROCEDURE uspGetAddress @City nvarchar(30) AS SELECT * FROM AdventureWorks.Person.Address WHERE City LIKE @City + '%' GO

Now the next time that the stored procedure is called by an end user it will use this new logic.

---