Brent Ozar thinks about consolidation:
I’ve got a BEGIN TRAN in there before the updates just so I can test the same queries repeatedly, and roll them back each time. The execution plan for the updates is quite nice: SQL Server divebombs into the supporting indexes:
Relatively few rows match, so our query does less than 1,000 logical reads – way less than there are pages in the table. In this case, separate UPDATE statements make sense.
Brent then continues with, but what do we do when we need to perform multiple independent scans of the same table? Read on for Brent’s answer, but definitely check out Thomas Franz’s comments, which indicate a potential complicating factor.