T-SQL Conditional Order By

Question

I am trying to write a stored procedure that returns a list of object with the sort order and sort direction selected by the user and passed in as sql parameters.

Le

Answer 1

declare @str varchar(max)
set @str = 'select * from Product order by ' + @sortOrder + ' ' + @sortDir
exec(@str)

Answer 2

You need a case statement, although I would use multiple case statements:

order by (case when @sortOrder = 'name' and @sortDir = 'asc' then name end)  asc,
         (case when @sortOrder = 'name' and @sortDir = 'desc' then name end) desc,
         (case when @sortOrder = 'created_date' and @sortDir = 'asc' then created_date end) asc,
         (case when @sortOrder = 'created_date' and @sortDir = 'desc' then created_date end) desc

Having four different clauses eliminates the problem of converting between types.

Answer 3

CASE is an expression that returns a value. It is not for control-of-flow, like IF. And you can't use IF within a query.

Unfortunately, there are some limitations with CASE expressions that make it cumbersome to do what you want. For example, all of the branches in a CASE expression must return the same type, or be implicitly convertible to the same type. I wouldn't try that with strings and dates. You also can't use CASE to specify sort direction.

SELECT column_list_please
FROM dbo.Product -- dbo prefix please
ORDER BY 
  CASE WHEN @sortDir = 'asc' AND @sortOrder = 'name' THEN name END,
  CASE WHEN @sortDir = 'asc' AND @sortOrder = 'created_date' THEN created_date END,
  CASE WHEN @sortDir = 'desc' AND @sortOrder = 'name' THEN name END DESC,
  CASE WHEN @sortDir = 'desc' AND @sortOrder = 'created_date' THEN created_date END DESC;

An arguably easier solution (especially if this gets more complex) is to use dynamic SQL. To thwart SQL injection you can test the values:

IF @sortDir NOT IN ('asc', 'desc')
  OR @sortOrder NOT IN ('name', 'created_date')
BEGIN
  RAISERROR('Invalid params', 11, 1);
  RETURN;
END

DECLARE @sql NVARCHAR(MAX) = N'SELECT column_list_please
  FROM dbo.Product ORDER BY ' + @sortOrder + ' ' + @sortDir;

EXEC sp_executesql @sql;

Another plus for dynamic SQL, in spite of all the fear-mongering that is spread about it: you can get the best plan for each sort variation, instead of one single plan that will optimize to whatever sort variation you happened to use first. It also performed best universally in a recent performance comparison I ran:

http://sqlperformance.com/conditional-order-by

Answer 4

There are multiple ways of doing this. One way would be:

SELECT *
FROM
(
  SELECT
  ROW_NUMBER() OVER ( ORDER BY
  CASE WHEN @sortOrder = 'name' and @sortDir = 'asc' then name
  END ASC,
  CASE WHEN @sortOrder = 'name' and @sortDir = 'desc' THEN name
  END DESC,
  CASE WHEN i(@sortOrder = 'created_date' and @sortDir = 'asc' THEN created_date
  END ASC,
  CASE WHEN i(@sortOrder = 'created_date' and @sortDir = 'desc' THEN created_date
  END ASC) RowNum
  *
)
order by 
RowNum

You can also do it using dynamic sql.

Answer 5

I stumbled on this when I was trying to do a similar thing, however the select statement I was creating includes a rather large and ugly string concatenation which severely limited my ability to use a dynamic SQL approach. If you have simple search cases, this is a decent solution.

That being said, another way to do this in SQL server specifically is with a table variable. This requires more overhead and complexity but it also gives you a lot of flexibility.

DECLARE @RawProducts TABLE (
    product_id int, 
    name varchar(50), 
    value int, 
    created_date datetime
)
INSERT INTO @RawProducts
SELECT * FROM [Product]

IF @sortOrder = 'name' AND @sortDir = 'asc' BEGIN
    SELECT * FROM @RawProducts
    ORDER BY [name] ASC
END

IF @sortOrder = 'name' AND @sortDir = 'desc' BEGIN
    SELECT * FROM @RawProducts
    ORDER BY [name] desc
END

IF @sortOrder = 'created_date' AND @sortDir = 'asc' BEGIN
    SELECT * FROM @RawProducts
    ORDER BY [created_date] ASC
END

IF @sortOrder = 'created_date' AND @sortDir = 'desc' BEGIN
    SELECT * FROM @RawProducts
    ORDER BY [created_date] desc
END

One drawback to this methodology is that you will need to add a case block for each and every case you want to order by but you would have to do that with any solution that does not involve dynamic SQL.

The only time I would recommend this method is if you have a relatively small data set and you have easy to discern search cases.