Почему внутри else не видит переменную в declare?

Question

[MuffinLover]

Код

CREATE OR REPLACE FUNCTION check_material_availability()
    RETURNS TRIGGER AS
$$
DECLARE
    required_materials RECORD;
    available_quantity INTEGER;
BEGIN
    FOR required_materials IN
        SELECT item_id, count
        FROM service_types_needed_items
        WHERE service_type_id = NEW.service_type_id
    LOOP
        SELECT quantity
        INTO available_quantity
        FROM storage_items si
                 JOIN storage s ON s.outlet_id = (SELECT accept_outlet_id FROM orders WHERE id = NEW.order_id)
        WHERE item_id = required_materials.item_id
          AND storage_id = s.id;

        IF available_quantity IS NULL THEN
            available_quantity := 0;
        END IF;

        IF available_quantity < required_materials.count THEN
            RAISE EXCEPTION 'Not enough materials available on the storage for this service order. Item ID: %, Required Count: %, Available Count: %', required_materials.item_id, required_materials.count, available_quantity;
        ELSE
            RAISE NOTICE 'Material available on the storage for this service order. Item ID: %, Required Count: %, Available Count: %', required_materials.item_id, required_materials.count, available_quantity;
            UPDATE storage_items
            SET quantity = quantity - required_materials.count
            FROM storage_items
                     JOIN storage s ON storage_items.storage_id = s.id
                     JOIN service_types_needed_items m ON storage_items.item_id = m.item_id
            WHERE storage_id = s.id
              AND item_id = required_materials.item_id;
        END IF;
    END LOOP;

    RETURN NEW;
END;
$$ LANGUAGE plpgsql;


CREATE OR REPLACE TRIGGER check_material_availability_trigger
    BEFORE INSERT
    ON service_orders
    FOR EACH ROW
EXECUTE FUNCTION check_material_availability();

почему на 29ой строчке(там где else) перестает видеть required_materials
ERROR: relation "required_materials" does not exist