Question

I have the following snippet from a SQL statements

ROW_NUMBER() OVER (ORDER BY CASE
    WHEN @SortBy = 'column1 ASC' THEN cast(column1 AS sql_variant)
    WHEN @SortBy = 'column2 ASC' THEN cast(column2 AS sql_variant)
    WHEN @SortBy = 'column3 ASC' THEN cast(column3 AS sql_variant)
    WHEN @SortBy = 'column4 ASC' THEN cast(column4 AS sql_variant)
    ELSE NULL
END ASC,
CASE
    WHEN @SortBy = 'column1 DESC' THEN cast(column1 AS sql_variant)
    WHEN @SortBy = 'column2 DESC' THEN cast(column2 AS sql_variant)
    WHEN @SortBy = 'column3 DESC' THEN cast(column3 AS sql_variant)
    WHEN @SortBy = 'column4 DESC' THEN cast(column4 AS sql_variant)
    ELSE NULL
END DESC) AS RowNumber

It works, but it’s quite repetitive, is there a way to make the ASC/DESC dynamic as well, so I don’t need the duplicated CASE statement?

Answer 1

One way you could do this would be to define the column alias at a different level so you can reference it twice without repeating the expression.

SELECT *,
       Row_number() OVER (ORDER BY 
                 CASE WHEN @SortBy LIKE '% ASC' THEN sort_col END ASC, 
                 CASE WHEN @SortBy LIKE '% DESC' THEN sort_col END DESC) AS RowNumber
FROM   YourTable
       CROSS APPLY (SELECT CASE
                             WHEN @SortBy LIKE 'column1 %' THEN Cast(column1 AS SQL_VARIANT)
                             WHEN @SortBy LIKE 'column2 %' THEN Cast(column2 AS SQL_VARIANT)
                             WHEN @SortBy LIKE 'column3 %' THEN Cast(column3 AS SQL_VARIANT)
                             WHEN @SortBy LIKE 'column4 %' THEN Cast(column4 AS SQL_VARIANT)
                           END) C(sort_col) 

I would consider using dynamic SQL for this instead though. This kind of catch all query will kill the idea of getting a good plan that can use indexes to avoid a sort.