I run into an issue today with PostgreSQL. I had manually entered a row into a table and it caused the primary key to fall out of sequence.
SQLSTATE: Unique violation: 7 ERROR: duplicate key value violates unique constraint...
To reset the primary key sequence ID on the PostgreSQL table I used the
SELECT setval(pg_get_serial_sequence('table_name_here', 'id'), COALESCE((SELECT MAX(id) + 1 FROM table_name_here), 1), false);
Source: How to reset postgres’ primary key sequence when it falls out of sync?