我的教授希望我们为我们的数据库类填写此代码中的一些空白。我认为我做得对，但我不确定我是否像我们刚刚开始讨论这个话题一样。如果有人能给我一些指导或有用的资料，我不知道从哪里开始第五个约束（IC5）。
SPOOL ddl.out
SET ECHO ON
--
-- Author:
--
-- IMPORTANT: use the names IC-1, IC-2, etc. as given below.
-- --------------------------------------------------------------------
DROP TABLE Orders CASCADE CONSTRAINTS;
DROP TABLE OrderLine CASCADE CONSTRAINTS;
--
CREATE TABLE Orders
(
orderNum INTEGER PRIMARY KEY,
priority CHAR(10) NOT NULL,
cost INTEGER NOT NULL,
/*
IC1: The priority is one of: high, medium, or low
*/
CHECK priority=('high' OR 'medium' OR 'low'),
/*
IC2: The cost of a high priority order is above 2000.
*/
CHECK priority='high' AND cost>2000,
/*
IC3: The cost of a medium priority order is between 800 and 2200 (inclusive).
*/
CHECK priority='medium' AND cost BETWEEN 800 AND 2200,
/*
IC4: The cost of a low priority order is less than 1000.
*/
CHECK priority='low' AND cost<1000,
);
--
--
CREATE TABLE OrderLine
(
orderNum INTEGER,
lineNum INTEGER,
item CHAR (10) NOT NULL,
quantity INTEGER,
PRIMARY KEY (orderNum, lineNum),
/*
IC5: Every order line must belong to an order in the Order table.
Also: if an order is deleted then all its order lines must be deleted.
IMPORTANT: DO NOT declare this IC as DEFERRABLE.
*/
<<< YOUR SQL CODE GOES HERE >>>
);
--
-- ----------------------------------------------------------------
-- TESTING THE SCHEMA
-- ----------------------------------------------------------------
INSERT INTO Orders VALUES (10, 'high', 2400);
INSERT INTO Orders VALUES (20, 'high', 1900);
INSERT INTO Orders VALUES (30, 'high', 2100);
INSERT INTO Orders VALUES (40, 'medium', 700);
INSERT INTO Orders VALUES (50, 'low', 1100);
INSERT INTO Orders VALUES (60, 'low', 900);
SELECT * from Orders;