Lowell (8/6/2013)
well in general, "particular column does not a character" would mean a NOT LIKE '%X%' pr PATINDEX =0, right?, so that would requre a table scan of all rows, so i'm no suprised it has a big impact; every value has to be evaluated.
And furthermore, it requires a full scan of every column value, which is very expensive if the full rules of Unicode must be applied. Which they must, unless any of the below are true:
1) You have a binary collation.
2) The column is varchar and you have an SQL collation.
[font="Times New Roman"]Erland Sommarskog, SQL Server MVP, www.sommarskog.se[/font]