Stored procedure output parameters or return values - Part 20

In this video, we will
1. Understand what are stored procedure return values
2. Difference between stored procedure return values and output parameters
3. When to use output parameters over return values

Before watching this video, please watch
Part 18 - Stored procedure basics in sql server
Part 19 - Stored procedures with output parameters







What are stored procedure status variables?
Whenever, you execute a stored procedure, it returns an integer status variable. Usually, zero indicates success, and non-zero indicates failure. To see this yourself, execute any stored procedure from the object explorer, in sql server management studio. 
1. Right Click and select 'Execute Stored Procedure
2. If the procedure, expects parameters, provide the values and click OK.
3. Along with the result that you expect, the stored procedure, also returns a Return Value = 0

So, from this we understood that, when a stored procedure is executed, it returns an integer status variable. With this in mind, let's understand the difference between output parameters and RETURN values. We will use the Employees table below for this purpose.




The following procedure returns total number of employees in the Employees table, using output parameter - @TotalCount.
Create Procedure spGetTotalCountOfEmployees1
@TotalCount int output
as
Begin
Select @TotalCount = COUNT(ID) from tblEmployee
End

Executing spGetTotalCountOfEmployees1 returns 3.
Declare @TotalEmployees int
Execute spGetTotalCountOfEmployees @TotalEmployees Output
Select @TotalEmployees

Re-written stored procedure using return variables
Create Procedure spGetTotalCountOfEmployees2
as
Begin
return (Select COUNT(ID) from Employees)
End

Executing spGetTotalCountOfEmployees2 returns 3.
Declare @TotalEmployees int
Execute @TotalEmployees = spGetTotalCountOfEmployees2
Select @TotalEmployees

So, we are able to achieve what we want, using output parameters as well as return values. Now, let's look at example, where return status variables cannot be used, but Output parameters can be used.

In this SP, we are retrieving the Name of the employee, based on their Id, using the output parameter @Name.
Create Procedure spGetNameById1
@Id int,
@Name nvarchar(20) Output
as
Begin
Select @Name = Name from tblEmployee Where Id = @Id
End

Executing spGetNameById1, prints the name of the employee
Declare @EmployeeName nvarchar(20)
Execute spGetNameById1 3, @EmployeeName out
Print 'Name of the Employee = ' + @EmployeeName

Now let's try to achieve the same thing, using return status variables.
Create Procedure spGetNameById2
@Id int
as
Begin
Return (Select Name from tblEmployee Where Id = @Id)
End

Executing spGetNameById2 returns an error stating 'Conversion failed when converting the nvarchar value 'Sam' to data type int.'. The return status variable is an integer, and hence, when we select Name of an employee and try to return that we get a converion error. 

Declare @EmployeeName nvarchar(20)
Execute @EmployeeName = spGetNameById2 1
Print 'Name of the Employee = ' + @EmployeeName

So, using return values, we can only return integers, and that too, only one integer. It is not possible, to return more than one value using return values, where as output parameters, can return any datatype and an sp can have more than one output parameters. I always prefer, using output parameters, over RETURN values.

In general, RETURN values are used to indicate success or failure of stored procedure, especially when we are dealing with nested stored procedures.Return a value of 0, indicates success, and any nonzero value indicates failure.

Difference between return values and output parameters