Constraint violation in a trusted constraint I have a table with a constraint on it that has an existing record that is in violation of that constraint.  While this is possible if someone applied the constraint without a check and after violation data was inserted, how would it be possible that the is_not_trusted flag is zero in the sys.foreign_keys table?

This is the situation I currently have, a data violation on a foreign key where the is_not_trusted flag is zero.  I thought that was essentially the flag that confirms whether the constraint has been enforced 'religiously'.

Thanks
From comments:
This might happen due to the the value physically written on the page being incorrect (data corruption). Or a bug in the product (probably less likely but possible). Run DBCC CHECKDB to see if that finds any issues. – Martin Smith Jun 18 '16 at 0:07
3
Along Martin's comment - did the data get into the table via MERGE? Here is one bug (closed as &quot;Won't Fix&quot;) that can do exactly this, and another bug (also &quot;Won't Fix&quot;). If you need more reasons to avoid MERGE, see this article. – Aaron Bertrand♦ Jun 18 '16 at 3:21