Query.sql

SELECT *
FROM "Users"
LEFT JOIN "Administrators" AS a ON "Users".Id = "Administrators".UserId

Tables.sql

CREATE TABLE "Users"
(
	"Id" UUID NOT NULL,
	"Username" VARCHAR(255),
	"Password" BYTEA,
	"Firstname" VARCHAR(255),
	"Lastname" VARCHAR(255),
	"CreatedOn" TIMESTAMP,
	PRIMARY KEY ("Id")
);

CREATE TABLE "Administrators"
(
	"UserId" UUID NOT NULL,
	PRIMARY KEY ("UserId")
);

ALTER TABLE "Administrators" ADD CONSTRAINT "Administrators_UserId" FOREIGN KEY ("UserId") REFERENCES "Users";