>Hilmar, we don't use views but we've sort pkey type of field. but every time we add record we check existence such pkey and add only if it's not there so no duplicate records issue here.
Well, I may very well be on a wrong track, but you would get a similar situation if you
update MyTable set SomeField = m.SomeValue;
where KeyField = m.KeyValue
In other words, the field you think is the key field should, indeed, be unique - or otherwise you'll be updating several records at a time.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
