Behavior of Serial Type Primary Keys in PostgreSQL

One cause of the ERROR: duplicate key value violates unique constraint error in PostgreSQL is that the sequence is not properly updated when values are manually assigned to a Serial type primary key. This happens because the default nextval is not called. To resolve this issue, you need to set the current maximum value of the primary key in the table to the sequence object. Specifically, by using the setval function to adjust the sequence object value, INSERT operations will execute correctly.