Adding Non clustered index

Question

So the current query I have takes long time to run. When i run execution plan, it shows: Table Insert (#tempdata), Cost: 99%. I realized i need to add non clustered index to run the query fast. So I have added this line of code but still there is no difference:

create nonclustered index #temp_index 
  on [dbo].#tempData ([class_room]) include ([class_name],[class_floor],[class_building])

This is the current query I have:

IF OBJECT_ID('tempdb..#tempdata') IS NOT NULL DROP TABLE #tempdata

    SELECT [class_room][class_name],[class_floor],[class_building]
    INTO #tempdata
    FROM class_info x

create nonclustered index #temp_index 
   on [dbo].#tempData ([class_room]) include ([class_name],[class_floor],[class_building])

;with cte1 as(
SELECT [class_room][class_name],[class_floor],[class_building]
FROM #tempdata
WHERE class_room <> '')  

select * from cte1

Answer 1

This is a bit long for a comment.

Can you explain why you are not just running this code?

SELECT [class_room], [class_name], [class_floor], [class_building]
FROM class_info x
WHERE class_room <> '';

If performance is an issue, I first would recommend getting rid of unnecessary reads and writes -- such as creating a temporary table.