Luis Cazares (10/1/2014)
You might be experiencing a problem described by Jeff Moden in the following article:http://www.sqlservercentral.com/articles/Performance+Tuning/62278/
I'm not sure how you tried to do the update with XML PATH, but it might not be the cause of the problem.
UPDATE t
SET col2 = col2 + STUFF( (SELECT ',' + f.col4
FROM @tbl_from f
WHERE t.col1 = f.col3
FOR XML PATH('')), 1, 1, '')
FROM @tbl_to t
Thanks for putting me on the right track, that article was extremely useful!
One thing, I've added a 'where exists' to only update relevant results..
UPDATE t
SET col2 = col2 + STUFF( (SELECT ',' + f.col4
FROM @tbl_from f
WHERE t.col1 = f.col3
FOR XML PATH('')), 1, 1, '')
FROM @tbl_to t
WHERE exists (SELECT 1 FROM @tbl_from f WHERE f.sessionid = t.sessionid)
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