CREATE TABLE worktime (
  id SERIAL PRIMARY KEY,
  date date NOT NULL,
  name varchar(50) NOT NULL,
  hours integer
);

INSERT INTO worktime (date, name, hours) VALUES('2019-05-01','Андрей',8);
INSERT INTO worktime (date, name, hours) VALUES('2019-05-01','Василий',11);
INSERT INTO worktime (date, name, hours) VALUES('2019-05-02','Роман',7);
INSERT INTO worktime (date, name, hours) VALUES('2019-05-05','Андрей',6);
INSERT INTO worktime (date, name, hours) VALUES('2019-05-10','Роман',11);
INSERT INTO worktime (date, name, hours) VALUES('2019-06-01','Василий',6);

SELECT name, SUM(hours) as sum_hours FROM worktime WHERE date BETWEEN '2019-05-01' AND '2019-05-05' GROUP BY name;