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Posted by Erland Sommarskog on 02/25/07 23:20
C10B (tswalton@gmail.com) writes:
> I have a table with several million rows.
> Each row is simply the date and time a certain page was viewed.
>
> eg
> page1 1-1-00
> page2 2-1-00
> page1 16-1-00
> page1 17-1-00
> page2 19-1-00
>
> I now need to find the most popular pages so I do this...
>
> SELECT TOP 10 COUNT(*) AS mycount FROM tblPageViews
> GROUP BY place ORDER BY COUNT(place) DESC
>
> ...which gives me the top 10 most viewed pages
>
> big problem - this is getting slower and slower as the table grows and
> grows.
>
> what should I do?
A non-clustered index on place would help, as SQL Server then only
would have to scan that index, and not the entire difference. But it
seems that the table has two columns. In such case, the index would not
reduce execution time that much.
A better alternative may be to define an indexed view that maintains
the count:
CREATE TABLE pagehits (pageid varchar(20) NOT NULL,
viewtime datetime NOT NULL,
PRIMARY KEY (pageid, viewtime)
)
go
CREATE VIEW pagecount WITH SCHEMABINDING AS
SELECT pageid, cnt = COUNT_BIG(*)
FROM dbo.pagehits
GROUP BY pageid
go
CREATE UNIQUE CLUSTERED INDEX pagecount_ix ON pagecount(pageid)
go
SELECT TOP 10 pageid, cnt
FROM pagecount WITH (NOEXPAND)
ORDER BY cnt
go
DROP VIEW pagecount
DROP TABLE pagehits
I added the NOEXPAND hint to the query, since it's only on Enterprise
Edition, the optimizer considers indexed views.
Note that this could have effect on performance when writing to the table.
--
Erland Sommarskog, SQL Server MVP, esquel@sommarskog.se
Books Online for SQL Server 2005 at
http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx
Books Online for SQL Server 2000 at
http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx
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