CREATE TABLE IF NOT EXISTS "boathouse" (
    "id" INTEGER PRIMARY KEY AUTOINCREMENT,
    "boat_id" INTEGER NOT NULL REFERENCES boat(id),
    "aisle" TEXT NOT NULL CHECK (aisle in ('water', 'middle', 'mountain')),
    "side" TEXT NOT NULL CHECK(side IN ('mountain', 'water')),
    "level" INTEGER NOT NULL CHECK(level BETWEEN 0 AND 3),
    CONSTRAINT unq UNIQUE (aisle, side, level) -- only 1 boat allowed to rest at each space 
);