Was the Tempdb log previously capped?
No, it wasn't, but it is now (10 GB).
@ChrisM@Work
Number of recs returned by your SELECT version of the query is unknown but large...it has now been running for 28 minutes, no 34 minutes; and is still going!!
What does SELECT PatientKey = P.PatientKey, AgeKey = PM.AgeKey ... mean - in a SELECT query that is? are the assignments just ignored?
Hmm, just looked at the PatienMonths table - it has 47303750 records and occupies 2,469.805 MB data space and 816.430 MB index space!
MarkD