Creating sequence in an existing table. PostgreSQL

creating-sequence-postgres.sql

/*
  objects_id_object_seq - sequence name
  objects               - table name
  id_object             - ID field name
  seq                   - standard postfix

Doc for setval() and nextval(): https://www.postgresql.org/docs/current/functions-sequence.html
*/

CREATE SEQUENCE IF NOT EXISTS objects_id_object_seq; -- IF NOT EXISTS is works only in Postgres 9.5+

SELECT setval(
  'objects_id_object_seq',
  (SELECT max(id_object) FROM objects)
);

ALTER TABLE objects ALTER COLUMN id_object SET DEFAULT nextval('objects_id_object_seq');

Nice, Very Good

Is there a reason for the increment in the maximum value of id_object? Wouldn't SELECT setval('objects_id_object_seq', (SELECT max(id_object) FROM objects)); do the same thing while being simpler and omitting the false value?

Is there a reason for the increment in the maximum value

You're right, there's no reason. Fixed.

Also consider associating the sequence with the table column:

ALTER SEQUENCE IF EXISTS objects_id_object_seq OWNED BY objects_id_object_seq.id_object;

See OWNED BY table_name.column_name for details.