Michael Valentine Jones (9/7/2012)

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You haven't provided enough information for anyone to begin to answer that question.

You should just try each way to see which is faster.

dwilliscp (9/7/2012)

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The problem with that is.. before the second run I would need to make sure the data is flushed from memory... not sure how to do that. Otherwise the second run should always be faster since it does not have hard drive I/O.

dwilliscp (9/7/2012)

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The problem with that is.. before the second run I would need to make sure the data is flushed from memory... not sure how to do that. Otherwise the second run should always be faster since it does not have hard drive I/O.

CHECKPOINT;
DBCC DROPCLEANBUFFERS;

dwilliscp (9/7/2012)

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To write new data using three outer joins or to use one outer join, and get most of the data, then use three updates to load the other three columns?

Alexander Suprun (9/7/2012)

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Usually the 1st approach is faster.
If any of these 3 columns have variable length (say varchar) then your update statement will cause a lot of page splits and therefore fragmentation.

dwilliscp (9/10/2012)

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I did run some tests.. but the results were not steady.. there is a lot of activity on this box. The updates do tend to have less variation, thus it can take 5% longer or up to 20% less time.. depending on the test. Again due to the load on the box, I just do not put any faith in the tests.

All the fields from the join are 50 - 200 varchar. So that could explain why this had the widest variation of run times. So since we have I/O pressure.. on this box and the production one this will get released too, I am going to go with the updates.