Resetting ID Sequence in PostgreSQL

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-- Latest Inserted ID
SELECT MAX(IDFIELD) FROM TABLENAME;

-- The id that will be assigned to the upcoming data tulip.
-- The result shoult be Latest ID + 1
SELECT nextval('TABLENAME_ID_SEQ');

BEGIN;
LOCK TABLE TABLENAME IN EXCLUSIVE MODE;
SELECT setval('TABLENAME_ID_SEQ', COALESCE((SELECT MAX(IDFIELD)+1 FROM TABLENAME), 1), false);
COMMIT;