Constraint between tables in SQL Server, deleting one should delete the other

Question

I am creating two tables RegistrationHeader and RegistrationDetail. How can i add a constraint that when i delete RegistrationHeader table to automaicaly delete the RegistrationDetail table.

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)
);

Thanks for the help!

Answer 1

You will need to

1) Set up foreign key relations between RegistrationHeader.RegistrationNo and RegistrationDetail.RegistrationNo

2) Add ON DELETE CASCADE to RegistrationDetail Foreign Key definition

I haven't tested this, but I believe this should be what you're looking for in SQL Server

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

Answer 2

Constrains are affecting only database columns such as primary/foreign keys or regular columns, not whole tables. You can add OnDelete or OnUpdate constraints for foreign keys to delete/keep the refrences from one table to other but not the whole table. That is mixing DML (select,update,insert,delete) with DDL (create,drop). Try to read more about DML and DDL .

Here's a good article about that