Wie erstelle ich eine Prüfeinschränkung für mehrere Tabellen?

Der beste Ort, um die Datenintegrität durchzusetzen, ist die Datenbank. Seien Sie versichert, dass einige Entwickler, absichtlich oder nicht, einen Weg finden werden, inkonsistente Dinge in die Datenbank zu schleichen, wenn Sie sie zulassen!

Hier ist ein Beispiel mit Check Constraints:

CREATE FUNCTION dbo.SignupMismatches()
RETURNS int
AS BEGIN RETURN (
    SELECT count(*)
    FROM Shift s
    LEFT JOIN EventVolunteer ev
    ON ev.EventId = s.EventId
    AND ev.VolunteerId = s.VolunteerId
    WHERE ev.Id is null
) END
go
ALTER TABLE Shift ADD CONSTRAINT chkSignup CHECK (dbo.SignupMismatches() = 0);
go
CREATE FUNCTION dbo.OverlapMismatches()
RETURNS int
AS BEGIN RETURN (
    SELECT count(*)
    FROM Shift a
    JOIN Shift b
    ON a.id <> b.id
    AND a.Start < b.[End]
    AND a.[End] > b.Start
    AND a.VolunteerId = b.VolunteerId
) END
go
ALTER TABLE Shift ADD CONSTRAINT chkOverlap CHECK (dbo.OverlapMismatches() = 0);

Hier sind einige Tests für die neuen Datenintegritätsprüfungen:

insert into Volunteer (name) values ('Dubya')
insert into Event (name) values ('Build Wall Around Texas')

-- Dubya tries to build a wall, but Fails because he's not signed up
insert into Shift (VolunteerID, EventID, Description, Start, [End]) 
    values (1, 1, 'Dunbya Builds Wall', '2010-01-01', '2010-01-02')

-- Properly signed up?  Good
insert into EventVolunteer (VolunteerID, EventID) 
    values (1, 1)
insert into Shift (VolunteerID, EventID, Description, Start, [End]) 
    values (1, 1, 'Dunbya Builds Wall', '2010-01-01', '2010-01-03')

-- Fails, you can't start the 2nd wall before you finished the 1st
insert into Shift (VolunteerID, EventID, Description, Start, [End]) 
    values (1, 1, 'Dunbya Builds Second Wall', '2010-01-02', '2010-01-03')

Hier sind die Tabellendefinitionen:

set nocount on
if OBJECT_ID('Shift') is not null
    drop table Shift
if OBJECT_ID('EventVolunteer') is not null
    drop table EventVolunteer
if OBJECT_ID('Volunteer') is not null
    drop table Volunteer
if OBJECT_ID('Event') is not null
    drop table Event
if OBJECT_ID('SignupMismatches') is not null
    drop function SignupMismatches
if OBJECT_ID('OverlapMismatches') is not null
    drop function OverlapMismatches

create table Volunteer (
    id int identity primary key
,   name varchar(50)
)
create table Event (
    Id int identity primary key
,   name varchar(50)
)
create table Shift (
    Id int identity primary key
,   VolunteerId int foreign key references Volunteer(id)
,   EventId int foreign key references Event(id)
,   Description varchar(250)
,   Start datetime
,   [End] datetime
)
create table EventVolunteer (
    Id int identity primary key
,   VolunteerId int foreign key references Volunteer(id)
,   EventId int foreign key references Event(id)
,   Location varchar(250)
,   [Day] datetime
,   Description varchar(250)
)