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I've seen the following technique in several beginner code samples for demonstrating SQL Server 2005's ability to return paged results.
I've added the TotalRows = Count(*) OVER() line to demonstrate how return the total rows returned above and beyond the row count for the paged set. This removes the need for a second query to get the total rows available for paging techniques in your application. In your application, just check to make sure your resultset has records, then just grab the first record and retrieve its TotalRows column value.
Notice that in this query, the JOIN between the Orders table and the Users table is being run across all records that are found NOT just the records returned in the paged set.
declare @StartRow int declare @MaxRows int
select @StartRow = 1 select @MaxRows = 10
select * from (select o.*,u.FirstName,u.LastName, TotalRows=Count(*) OVER(), ROW_NUMBER() OVER(ORDER BY o.CreateDateTime desc) as RowNum from Orders o , Users u WHERE o.CreateDateTime > getdate() -30 AND (o.UserID = u.UserID) ) WHERE RowNum BETWEEN @StartRow AND (@StartRow + @MaxRows) -1
If you adjust your query as follows, you will see a substantial boost in performance. Notice this query only performs the join on the returned resultset which is much, much smaller.
SELECT MyTable.*,u.FirstName,u.LastNameFROM (SELECT o.*, TotalRows=Count(*) OVER(), ROW_NUMBER() OVER(ORDER BY o.CreateDateTime desc) as RowNum FROM Orders o WHERE o.CreateDateTime > getdate() -30 ) as MyTable, Users uWHERE RowNum BETWEEN @StartRow AND (@StartRow + @MaxRows) -1 and (MyTable.UserID = u.UserID)
Having recently reviewed ways to speed up the paging grids at EggHeadCafe (they were never slow but I'm always looking for ways to optimize things), I decided to put SQL Server's new paging mechanism to a test between itself and using standard queries in conjunction with TABLE variables. Across 5 different very large tables at EggHeadCafe, the TABLE variable option performed twice as fast as the suggested paging mechanism above. Why I didn't of think of why much sooner is beyond me...
When you look at the inner query in the paging sample above, you notice that it is pulling back the entire Orders record for every single record in the Orders table. Then, the outer query queries the inner table's results.
The TABLE variable sample stored procedure syntax doesn't perform the same JOINS as above. It is includedhere just to give you an idea of how you might write your own. Of course, depending on how often your data changes, you could even implement a cache of the primary keys to speed this up even more.
I saw the biggest performance gains when querying for pages deep in the result set. In our case, that was tens of thousands of pages deep.
CREATE PROCEDURE [dbo].[GetRecordsPaged]( @StartRow int, @MaxRows int)AS
declare @TotalRows bigint
declare @Pager table ( RowNumber int IDENTITY (1, 1) Primary key NOT NULL , RecordID bigint,
Primary Key Clustered(RowNumber))
-- Notice that this INSERT INTO query can get 100% of its results from the clustered primary key index.
INSERT INTO @Pager (RecordID)SELECT RecordIDFROM dbo.RecordORDER BY RecordID desc -- You can ORDER BY datetime columns if your primary key is not a number oriented column.
SELECT top 1 @TotalRows = COUNT(*) from @Pager -- Did this because it is a little faster than TotalRows=Count(*) OVER()
-- You would append your JOINS etc. to the result query below
SELECT Record.*, @TotalRows as TotalRowsFROM dbo.Record WHERE RecordID in (SELECT RecordID FROM @Pager i WHERE i.RowNumber BETWEEN @StartRow AND (@StartRow + @MaxRows) - 1)ORDER BY RecordID desc