I have 3 tables:
Create TABLE Subjects
(
SubjectID INT PRIMARY KEY NOT NULL IDENTITY(1,1),
SubjectName VARCHAR(20) NOT NULL,
ClassID VARCHAR(10) FOREIGN KEY REFERENCES Classes(ClassID) NOT NULL
);
Create TABLE Topic
(
TopicID INT PRIMARY KEY NOT NULL IDENTITY(1,1),
TopicName VARCHAR(100),
SubjectID INT FOREIGN KEY REFERENCES Subjects(SubjectID)
);
Create Table Worksheet
(
WorksheetName varchar(100) PRIMARY KEY,
TopicID INT Foreign KEY References Topic(TopicID),
Num_Q INT NOT NULL,
W_Type varchar(30)
);
Each one is a one to many relationship. When I try to delete from Subjects I get a foreign key constraint which is fine. What I want to know is how to get around this and perform a query to delete all relating aspects in a cascading style. I looked it up and there's but I am not sure how it works there seems to be multiple queries. Would it be better to create a trigger or is there a basic cascading function to do it all? I'm using visual studio to perform queries but not sure where the options to perform tasks like this are?
You can add the ON DELETE CASCADE right after the foreign key definition:
Create TABLE Subjects (
SubjectID INT PRIMARY KEY NOT NULL IDENTITY(1, 1),
SubjectName VARCHAR(20) NOT NULL,
ClassID VARCHAR(10) NOT NULL
FOREIGN KEY REFERENCES Classes(ClassID) ON DELETE CASCADE
);
You can also define it as a separate constraint, if you like, either within the CREATE TABLE statement or using ALTER TABLE ADD CONSTRAINT.
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