Answers for "delete from postgres table and reset id to 1"

truncate table in postgresql and reset id

TRUNCATE bigtable, fattable RESTART IDENTITY;

reset id sequence postgres

alter sequence <tableName>_id_seq restart with 1;
For an instance, we have a table named "groups" and we need to reset the id sequence with 1. 
alter sequence groups_id_seq restart with 1;