Question

我有一个包含Customer和WatchHistory表的数据库。客户只能在他的subscription_start之后和他的subscription_end之前观看电影。我尝试了以下方法：

ALTER TABLE WatchHistory
ADD CONSTRAINT ck_watch_date
  CHECK (watch_date > Customer.subscription_start AND watch_date < Customer.subscription_end)

但是我收到以下错误：

Msg 4104, Level 16, State 1, Line 3
The multi-part identifier "Customer.subscription_start" could not be bound.
Msg 4104, Level 16, State 1, Line 3
The multi-part identifier "Customer.subscription_end" could not be bound.

我的猜测是我必须使用联接，但我该把它放在哪里？以下不起作用：

ALTER TABLE WatchHistory INNER JOIN Customer
  ON WatchHistory.customer_mail_address = Customer.customer_mail_address
ADD CONSTRAINT ck_watch_date
  CHECK (watch_date > Customer.subscription_start AND watch_date < Customer.subscription_end)

Answer 1

执行此操作的一种方法是创建UDF，然后在UDF上创建约束。

您的代码示例（未经过测试，请测试一下） -

CREATE FUNCTION ufn_check_customerwatchhistory (
    @watch_date DATE
)
RETURNS VARCHAR(10)
AS
BEGIN
    IF EXISTS (SELECT 1 FROM Customer WHERE @watch_date > Customer.subscription_start AND @watch_date < Customer.subscription_end)
        return 'True'
    return 'False'
END

ALTER TABLE WatchHistory
ADD CONSTRAINT ck_watch_date
  CHECK (ufn_check_customerwatchhistory(watch_date) = 'True')

使用不同的表添加约束

1 个答案: