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Columns are different but are not marked as such! The highlighting of the differences on the script of an object is controlled by the comparison engine so if the comparison engine marks two objects as equal then nothing will be highlighted on the scripts of those objects even though there might be visible differences on the script. Why does this happen? The answer lies in the comparison options - there are a few options related to collation, nullability, replication, identity etc. that affect the column comparison. So if you have for example chosen to ignore the column collation then even though the column on the left might have a different collation from that on the right the columns will be marked as equal and therefore the collation difference on the script will not be highlighted.