Glad we could help. One other word of caution. You are selecting the Top 1 in that update clause, but you aren't ordering by anything. This could lead to unexpected/inconsistent results if you routinely have more than one EventID for each EntityID and DateTime. If you are sure that you DON'T ever have more than 1 EventID for any given EntityID or Datetime, then your query can be simplified to eliminate the subquery as so:

UPDATE @EntityDateTimes

SET EventID= EH.EventID

FROM @EntityDateTimes E

INNER JOIN tkEntityHistory EH ON E.EntityID=EH.EntityID AND E.[DateTime]=EH.[DateTime]

I'll leave it to someone else to gripe about the cursors :hehe: