Question

I’ve found out the following article about A More Efficient Method for Paging Through Large Result Sets

They say:

An optimizer trick that can also be used in this scenario is when a
single variable is set to a potential list of values, it will get
assigned the value of the last item in the list.

And then they provide the following sample:

CREATE  PROCEDURE [dbo].[usp_PageResults_NAI] 
(
    @startRowIndex int,
    @maximumRows int
)
AS

DECLARE @first_id int, @startRow int

-- A check can be added to make sure @startRowIndex isn't > count(1)
-- from employees before doing any actual work unless it is guaranteed
-- the caller won't do that

-- Get the first employeeID for our page of records
SET ROWCOUNT @startRowIndex
SELECT @first_id = employeeID FROM employees ORDER BY employeeid

-- Now, set the row count to MaximumRows and get
-- all records >= @first_id
SET ROWCOUNT @maximumRows

SELECT e.*, d.name as DepartmentName 
FROM employees e
   INNER JOIN Departments D ON
       e.DepartmentID = d.DepartmentID
WHERE employeeid >= @first_id
ORDER BY e.EmployeeID

SET ROWCOUNT 0

GO 

Based on the above mentioned article I have written the following T-SQL stored procedure:

CREATE PROCEDURE Find_Programs

    @programId INTEGER

AS

BEGIN

    SET NOCOUNT ON;
    DECLARE @SelectQuery NVARCHAR(2000)

    DECLARE @first_id INTEGER

    SET @SelectQuery = 'SELECT @first_id = bp.program_id FROM program bp WHERE  bp.program_id >= @programId ORDER BY bp.program_id'
    EXECUTE sp_Executesql @SelectQuery, N'@first_id INTEGER, @programId INTEGER', @first_id, @programId

    PRINT 'first_id: ' + CONVERT(VARCHAR(10),@first_id);

END

but when I run EXEC dbo.Find_Programs @programId = 0 I get no output. It seems like @first_id is not changing its value. Any ideas why?

Answer 1

Because you have not specified that @first_id is an output parameter- you are passing it into sp_Executesql, but not getting it back out. This article explains how to use output parameters with sp_Executesql.