Actual Number of Rows

Last Post 04 Nov 2011 08:21 AM by rerichards. 2 Replies.
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rerichards
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02 Nov 2011 09:28 AM
Running SQL Server 2008 Enterprise, SP1 CU7, 10.00.2766.

When executing a query with multiple joins, I get the following from the execution plan on a table, which is a Clustered Index Seek node in the execution plan:
Actual Number of Rows: 27779037
Estimated Number of Rows: 3486

When I exectute the following on the table upon which this clustered index seek was performed, I get 238,850.
SELECT COUNT(*) from dbo.MyTable

Now, I am sure someone is tempted to say, "Your statistics are out of date", or "You need to update statistics".

Okay, granted, I understand that may be an issue, but that is not the reason for this post, or answering my question, which is:

How can the Actual Number of Rows, (may I repeat, the Actual Number of Rows, not the Estimated Number of Rows) be 27,779,037 when the number of rows in the table are only 238,850?

Also, the node that gives these metrics, is the beginning node in the branch, that is, the node that gives an Actual Number of Rows of 27,779,037 is not fed by any other nodes, or incoming data nodes. It is the beginning node in the branch, not being fed by any other nodes.
gunneyk
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04 Nov 2011 07:58 AM
I would say it is most likely a bug. I have heard similar stories in the past but unfortunately don't have any links to hard facts. But I wonder if the operation is a nested loop in which the outer table may call the table with 238,850 rows many times in like a cartesian result?
rerichards
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04 Nov 2011 08:21 AM
Thanks for the reply gunneyk.

I suspected the same and have since opened a Microsoft Support Case. It is currently being looked at by a SQL Server Engineer.
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