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POCustom sorting and pagination over large tables
 

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    <p>I'm used to get benefits from ROW_NUMBER function in MS SQL Server scripts since 2005 version. But I noticed there is big performance disadvantage querying big tables using this function.</p> <p>Imagine table with four columns (a real table from external database has more columns, but I used only those to avoid complexity of example):</p> <pre><code>DECLARE TABLE StockItems ( Id int PRIMARY KEY IDENTITY(1,1), StockNumber nvarchar(max), Name nvarchar(max), [Description] nvarchar(max)) </code></pre> <p>I've written procedure for querying this table filled up by 200 000+ rows with following parameters:</p> <ul> <li>@SortExpression - name of column by which I want to sort</li> <li>@SortDirection - bit information (0=ascending, 1=descending)</li> <li>@startRowIndex - zero based index at which I want retrieve rows</li> <li>@maximumRows - number of rows to be retrieved</li> </ul> <p>Query:</p> <pre><code>SELECT sortedItems.Id ,si.StockNumber ,si.Name ,si.Description FROM (SELECT s.Id ,CASE WHEN @SortDirection=1 THEN CASE WHEN CHARINDEX('Name',@SortExpression)=1 THEN ROW_NUMBER() OVER (ORDER by s.Name DESC) WHEN CHARINDEX('StockNumber',@SortExpression)=1 THEN ROW_NUMBER() OVER (ORDER by s.StockNumber DESC) ELSE ROW_NUMBER() OVER (ORDER by s.StockNumber DESC) END ELSE CASE WHEN CHARINDEX('Name',@SortExpression)=1 THEN ROW_NUMBER() OVER (ORDER by s.Name ASC) WHEN CHARINDEX('StockNumber',@SortExpression)=1 THEN ROW_NUMBER() OVER (ORDER by s.StockNumber ASC) ELSE ROW_NUMBER() OVER (ORDER by s.StockNumber ASC) END END AS RowNo FROM stockItems s ) as sortedItems INNER JOIN StockItems si ON sortedItems.Id=si.Id ORDER BY sortedItems.RowNo </code></pre> <p>In situation when number of rows is growing rapidly, ROW_NUMBER became ineffective, because must sort all rows.</p> <p>Please can you help me to avoid this performance disadvantage and speed up the query?</p>
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