T-SQL Conditional Order By - sql

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.
Lets say I have a table of products with the following columns: product_id(int), name(varchar), value(int), created_date(datetime)
and parameters #sortDir and #sortOrder
I want to do something like
select *
from Product
if (#sortOrder = 'name' and #sortDir = 'asc')
then order by name asc
if (#sortOrder = 'created_date' and #sortDir = 'asc')
then order by created_date asc
if (#sortOrder = 'name' and #sortDir = 'desc')
then order by name desc
if (#sortOrder = 'created_date' and #sortDir = 'desc')
then order by created_date desc
I tried do it with case statements but was having problems since the data types were different. Anyone got any suggestions?

Answer 1

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 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

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 4

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