Question

我正在创建两个表RegistrationHeader和RegistrationDetail。如何添加一个约束，当我删除RegistrationHeader表以自动删除RegistrationDetail表时。

create table RegistrationHeader(
    RegistrationNo numeric
    ,BillingID varchar(30) not null
    ,RegistrationDate date not null
    ,PaymentType varchar check (PaymentType = 'CC' or PaymentType = 'PO' or PaymentType = 'Check') not null
    ,CCNumber numeric check(CCNumber >= 15 and CCNumber <=16)
    ,PONumber varchar(30)
    ,CheckNumber varchar(10)
    ,primary key(RegistrationNo)
    ,foreign key(BillingId) references Person(UserID) 
    ,constraint CC_CCNumber_constr check(
        (PaymentType = 'CC' and CCNumber is not null)
        or
        (PaymentType != 'CC' and CCNumber is null)
    )
    ,constraint PO_PONumber_constr check(
        (PaymentType = 'PO' and (PONumber is not null or PONumber != ''))
        or
        (PaymentType != 'PO' and PONumber is null)
    )
    ,constraint CheckNumber_type_constr check(PaymentType != 'Check' and CheckNumber is null)
);

create table RegistrationDetail(
    RegistrationNo numeric
    ,LineNumber numeric
    ,CourseID numeric(10) not null
    ,AttendeeID varchar(30) not null
    primary key(RegistrationNo,LineNumber)
);

感谢您的帮助！

Answer 1

你需要

1）在RegistrationHeader.RegistrationNo和RegistrationDetail.RegistrationNo

之间设置外键关系

2）将ON DELETE CASCADE添加到RegistrationDetail外键定义

我没有对此进行测试，但我相信这应该是您在 SQL Server

中寻找的内容

ALTER TABLE RegistrationDetail
ADD CONSTRAINT FK_RegistrationHeader_RegistrationDetail_Cascade
FOREIGN KEY (RegistrationNo) REFERENCES RegistrationDetail (RegistrationNo) ON DELETE CASCADE

Answer 2

约束只影响数据库列，例如主键/外键或常规列，而不是整个表。您可以为外键添加OnDelete或OnUpdate约束，以删除/保持从一个表到其他表但不是整个表的引用。这就是将DML（选择，更新，插入，删除）与DDL混合（创建，删除）。尝试详细了解DML和DDL。

Here's 一篇关于那篇的好文章

SQL Server中的表之间的约束，删除一个应该删除另一个

2 个答案: