When you create a table with a primary key or a unique constraint, Oracle automatically creates a unique index, to ensure that the column does not contain a duplicate value on that column; or so you have been told. It must be true because that is the fundamental tenet of an Oracle database, or for that matter, any database.
Well, the other day I was checking a table. There is a primary key on the column PriKey. Here are the rows:
Select PriKey from TableName;
I got two rows with the same value. The table does have a primary key on this column and it is enforced. I can test it by inserting another record with the same value - “1”:
SQL> insert into TableName values (1,…)