SQL Server性能问题

Question

I have this query in SQL Server 2012:

Select cat, dog, ant, pig, ItemId 
from dbo.Animals 
where cat <> 'sam' 
  and cat in ('bam', 'dam') 
order by pig

I have laid out below what I did and looked at execution plan and the performance time below.

1. No indexing - Table scan - 20 s

2. Clustered Index on ItemId - Clustered Index scan - 20 s

3. Non Clustered index on cat - Clustered Index scan [ Same as 2 ] - 20s

4. Non Clustered index on pig - Clustered Index scan [ Same as 2 ] - 20s

My questions is why is the performance the same in all scenarios?

Is Caching playing a factor ? I don't have permission to play with freeing cache and things like that currently. Can I try anything else from indexing perspective ?

Answer 1

Your where is redundant, because the conditions on cat only need the in .

I suspect the index can be used for the where clause but not for the order by . Hence, indexes can be used to optimize the search for the rows, but not for the final ordering. Presumably there is a large amount of data and that is taking the bulk of the time.