CREATE TABLE "teste" (
"id" int8 DEFAULT nextval('teste_id_seq'::regclass) NOT NULL,
"start_date" timestamp(6),
"end_date" timestamp(6),
CONSTRAINT "teste_pkey" PRIMARY KEY ("id")
)

INSERT INTO "teste" VALUES ('2019-3-17 17:38:23', '2019-3-18 17:40:00');
INSERT INTO "teste" VALUES ('2019-3-17 17:20:00', '2019-3-17 18:39:07');


select end_date-start_date from teste;
select sum(end_date-start_date) from teste;