CREATE OR REPLACE FUNCTION doc_periods(curt TIMESTAMP, counter integer)
returns void LANGUAGE plpgsql AS $$
BEGIN curt :='2018-04-19 00:00:00';
 counter := 1;
WHILE curt <'2018-04-29 23:59:59'
LOOP
IF date_part('dow',curt) in (6,7)
THEN insert into doc_periods(docid, periodbegin, periodend) values (counter, curt, curt + interval '24 hours');
curt := curt + interval '24 hours';
counter := counter + 1;
ELSE insert into doc_periods(docid, periodbegin, periodend) values (counter,curt + interval '9 hours',curt +interval '11 hours');
insert into doc_periods(docid, periodbegin, periodend) values (counter+1,curt+ interval '1 hour',curt + interval '6 hour 30 minute');
curt := curt + interval '24 hours';
counter := counter + 2;
END IF; end loop;
end;
$$