Msg 3728, Level 16, State 1, Line 1
‘%.*ls’ is not a constraint.
This error message appears when you try to DROP a constraint that either does not exist or to which you want to refer by a name under which no constraint is known in the database.
The T-SQL statement can be parsed, but causes the error at runtime.
Error of the Severity Level 15 are generated by the user and can be fixed by the SQL Server user. The constraint object must exist and you must refer to it by the correct name.
All versions of SQL Server
CREATE TABLE t
c1 INT NOT NULL CONSTRAINT DF_c1 DEFAULT 0
ALTER TABLE t
DROP CONSTRAINT DF_c11
DROP TABLE t
In the above example the error is raised by the typo in the constraint name.