Dynamic order by without using dynamic sql? - sql

Question

I have the following stored procedure which can be sorted ascending and descending on TemplateName,CreatedOn and UploadedBy. The following SP when runs doesnot sort records.if i replace 2,3,4 by columnname, i got an error message "Conversion failed when converting the nvarchar value 'Test Template' to data type int.".Please suggest how to achieve sorting.
CREATE PROCEDURE [dbo].[usp_SEL_GetRenderingTemplate]
(
#facilityID INT,
#sortOrder VARCHAR(5),
#sortExpression VARCHAR(100),
#errorCode INT OUTPUT
)
AS
BEGIN
SET NOCOUNT ON ;
BEGIN TRY
SET #sortOrder = CASE #sortOrder
WHEN 'Ascending' THEN 'ASC'
WHEN 'Descending' THEN 'DESC'
ELSE 'ASC'
END
SELECT TemplateID,
TemplateName,
CreatedOn,
( [user].LastName + ' ' + [user].FirstName ) AS UploadedBy
FROM Templates
INNER JOIN [user] ON [user].UserID = Templates.CreatedBy
WHERE facilityid = #facilityID
ORDER BY CASE WHEN #sortExpression = 'TemplateName'
AND #sortOrder = 'ASC' THEN 2
WHEN #sortExpression = 'CreatedOn'
AND #sortOrder = 'ASC' THEN 3
WHEN #sortExpression = 'UploadedBy'
AND #sortOrder = 'ASC' THEN 4
END ASC,
CASE WHEN #sortExpression = 'TemplateName'
AND #sortOrder = 'DESC' THEN 2
WHEN #sortExpression = 'CreatedOn'
AND #sortOrder = 'DESC' THEN 3
WHEN #sortExpression = 'UploadedBy'
AND #sortOrder = 'DESC' THEN 4
END DESC
SET #errorCode = 0
END TRY
BEGIN CATCH
SET #errorCode = -1
DECLARE #errorMsg AS VARCHAR(MAX)
DECLARE #utcDate AS DATETIME
SET #errorMsg = CAST(ERROR_MESSAGE() AS VARCHAR(MAX))
SET #utcDate = CAST(GETUTCDATE() AS DATETIME)
EXEC usp_INS_LogException 'usp_SEL_GetFacilityWorkTypeList',
#errorMsg, #utcDate
END CATCH
END

Answer 1

The dynamic ordering has to be of the same datatype. Here is an example of something that I use to case order three different datatypes - integer, date (ascending and descending), and string. This may not work for your situation, but at least you can see some techniques for casting to a common datatype.
...
ORDER BY
Case Parent.RankTypeID
When 0 Then dbo.Documents.Rank
When 1 Then Convert(int, dbo.Documents.DateStart, 112)
When 2 Then (1 - Convert(int, dbo.Documents.DateStart, 112))
When 3 Then Cast(dbo.Documents.Title as sql_variant)
End
Note:
112 is a date format of YYYYMMDD - useful for ordering.

Answer 2

We perform a similar sort of dynamic ordering in one of our products.
The only real different to your code is firstly, we don't use the live join.
We create a temporary table, so we can perform paging, and then apply the order.
We also use ints for ordering, cuts down on the overhead of string comparison.
It does make your SQL a bit longer, but this approach is definitely faster for the Query Optimiser. Also, and more importantly, I don't think you can mix types in Switch blocks, for ordering, so to follow your original code, you'd have to CONVERT all your data to the same time, which defeats the object :(
So you'd have
DECLARE #temp TABLE(ID int identity(1,1), TemplateID int, TemplateName nvarchar(100), CreatedOn datetime, UploadedBy nvarchar(100))
INSERT INTO #temp(TemplateID, TemplateName, CreatedOn, UploadedBy)
SELECT TemplateID,
TemplateName,
CreatedOn,
( [user].LastName + ' ' + [user].FirstName ) AS UploadedBy
FROM Templates
INNER JOIN [user] ON [user].UserID = Templates.CreatedBy
WHERE facilityid = #facilityID
Then:
IF #SortOrder = 1 --'ASC'
BEGIN
IF #sort = 2
Select *
From #Temp
Order by TemplateName ASC
ELSE IF #sort = 3
Select *
From #Temp
Order By CreatedBy ASC
-- and so on...
END
ELSE -- descending
BEGIN
-- Ad. Inf.
END
Delete
From #Temp
WHERE ID < #pageStart or ID > #pageStart + #pageSize

Answer 3

The following SP when runs doesnot
sort records.if i replace 2,3,4 by
columnname,
You shouldn't replace 2, 3, 4 in the ORDER BY clause by the column name. When you call the procedure just pass the column you want to sort by as the 3rd parameter.
EXEC [dbo].[usp_SEL_GetRenderingTemplate] 1,'Ascending','CreatedOn',#vErrorCode
The CASE will then evaluate the query to something like
...ORDER BY 3 DESC
which sorts the query by the 3rd column in the SELECT clause (i.e. CreatedOn)

Answer 4

The problem is that in CASE clauses the return values must have the same data type.
You can work around this problem by using multiple CASE statements http://www.extremeexperts.com/sql/articles/CASEinORDER.aspx
Or casting everything to the same data type.