Answers for "truncate psql"

restart identity cascade

TRUNCATE <table_name> RESTART IDENTITY CASCADE;
--RESTART will reset the identity sequence
--CASCADE all tables that have a foreign key reference to 
--table_name will be truncated as well

truncate table postgres

truncate my_table restart identity

postgres clear table

TRUNCATE [ TABLE ] [ ONLY ] name [ * ] [, ... ]
    [ RESTART IDENTITY | CONTINUE IDENTITY ] [ CASCADE | RESTRICT ]