Question

SQL Server Index Recommendation

Asked by: r_i_x

Have a transactional table like this (tblTrx):
TableID, int
ProductID, int
CreatedOn, datetime
Quantity, int

Size of table is getting to 2.5M records and will grow at about 1.5M/year.

Most queries are date related wanting to know what the product quantities were at a certain date so we generally query like this:

SELECT * FROM tblTable T
INNER JOIN
(SELECT ProductID, MAX(TableID) AS TableID FROM tblTrx WHERE CreatedOn > @TIMESTAMP GROUP BY ProductID) M
ON T.ProductID = M.ProductID
AND T.TableID = M.TableID

Clustered index is on TableID
Non-clustered index on CreatedOn

So, a couple questions:
1. Is this type of query optimal for getting this data?
2. Thoughts on indexes?

What I'm finding is that a lot of queries are doing Clustered Index Scans rather than Seeks and it's getting slow.

Thoughts?

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Asked On
2009-11-05 at 05:47:00ID24874321
Tags

SQL Server 2005

Topics

SQL Server 2005

,

SQL Server 2008

Participating Experts
3
Points
500
Comments
6

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Answers

 

by: chapmandewPosted on 2009-11-05 at 05:50:50ID: 25749377

If I were you, I would put this:

SELECT ProductID, MAX(TableID) AS TableID FROM tblTrx WHERE CreatedOn > @TIMESTAMP GROUP BY ProductID

Into a temp table, index the temp table, and then do the join on it instead.  

 

by: elimesikaPosted on 2009-11-05 at 05:51:12ID: 25749380

HI

I would add a non cluster index on :
TableID, ProductID, CreatedOn

 

by: r_i_xPosted on 2009-11-05 at 05:55:08ID: 25749420

chapmandew: you mean at time of query or daily job that would have: ProductID, TableID, Datetime?

elimesika: I will try that

 

by: chapmandewPosted on 2009-11-05 at 05:57:33ID: 25749449

SELECT ProductID, MAX(TableID) AS TableID
into #temp
FROM tblTrx WHERE CreatedOn > @TIMESTAMP GROUP BY ProductID

create clustered index idx_temptable_productidtableid on #temp(ProductID, TableID)

SELECT * FROM tblTable T
INNER JOIN
#temp M
ON T.ProductID = M.ProductID
AND T.TableID = M.TableID


from there, youll be in good shape.  even better if you add the indexes as suggested earlier...

 

by: molarPosted on 2009-11-05 at 06:06:33ID: 25749529

Creating indexes on ProductID and TableID will give you "index coverage" in that all the data you need can be found in the indexes themselves, so the database doesn't actually have to go to the data at all. This can sometimes speed things up.

Whether SQL uses indexes or table scans often depends on how much data your queries are returning. If your results bring back more than about 1-2% of the table, SQL Server will normally ignore the indexes and opt for a table scan anyway.

 

by: r_i_xPosted on 2009-11-24 at 05:39:07ID: 31650478

All gave valuable input. A combination of all and some other tweaking seems to have improved performance.

20120131-EE-VQP-002

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