Query problem with lookup column in SharePoint

Setup:

I have two lists on a SharePoint site, A and B. List A has a column 'b' that is a lookup to the ID field of list B. I have 500k+ records in A and about 6k records in B.

What works:

I am able to execute a query for items in list A using SharePoint web services, and am even able to filter the query based on a specific "lookup" value for column 'b'. For example, I can query for items in A whose column b matches 1234 (...<Value Type="Lookup">1234</Value>...), and so on.

What doesn't work:

The query does not work for items older than a specific date, even though my query does not involve dates in any way -- only the lookup column. Any query on data newer than two years old works fine, anything older than that fails. If I view items from the SharePoint web page they appear ok, and all the links from child records in B to parent records in A work just fine -- the lookup columns appear intact.

Question:

Is there some kind of maintenance task in SharePoint that can cause some underlying data to get corrupted that can prevent a query based on a lookup id to stop workin开发者_如何学Gog, like a system restore, etc? In other words, the lookup column data appears correct on the surface in the web browser. But does SharePoint represent this value with a GUID or other invisible data that might be out of sync or stale?

Thanks.

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Maybe you are hitting another limit; the maximum number of items retrieved in a query?

See list throttling

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Try querying by the ID by adding the LookupId=”TRUE” attribute to your FieldRef element. http://abstractspaces.wordpress.com/2008/05/05/caml-query-lookup-field-by-id-not-by-value/

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The problem appears to be related to the fact that the column in question was indexed. When I removed the index everything started working. When I reapplied the index, everything kept on working. I'm attributing this problem to a corrupt index.