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');