You can run the following query to see what the primary key is for this table.
sp_pkeys 'supervisor'
Primary Keys are usually set on a table to indicate the unique identifier for a record. You wouldn't want to have 2 records in the same table with the same unique identifier (but representing 2 different things).
> Is this wrong?
It is wrong to insert a new record in a table with a primary key that already exists in the table.
>Why is this wrong?
It's wrong because the Primary Key represents the unique identifier. For something to be unique, by definition, means you cannot have something else exactly like it.
For example, let's say you have a People table. In this imaginary table, you have name, BirthDate, EyeColor, etc... If the Name was the unique identifier (REALLY bad idea), then you wouldn't be able to uniquely identify a single record if there are duplicates. So, you have 2 people in the table with the same name, but representing 2 different people. If you tried to update the EyeColor for one person, both would get updated. You would have incorrect data. Now, suppose, with the same table, NAME was a primary key. You wouldn't be able to insert 2 records (for 2 people) with the same name. The database would prevent it. This keeps your data clean.
-George
Strong and bitter words indicate a weak cause. - Fortune cookie wisdom