SQL Server 2014, trigger : how to iterate over deleted rows? - sql-server

Question

ATTENTION! Using trigger is necessary for me! The only way needed for me to perform following task - is to use trigger!
The question is - I need a trigger, which would be called on rowS deletion in a certain table. The thing trigger must do - iterate over every deleted
row, and perform some code - depending on current iterated row values.
for example, I made this trigger, which works when I delete one row
by command
DELETE FROM books WHERE id=5
the trigger is here:
GO
CREATE TRIGGER onBookDelete ON books
INSTEAD OF DELETE
AS
DECLARE #book_id int
BEGIN
SET NOCOUNT ON;
SELECT id FROM deleted
SET #book_id = (SELECT id FROM deleted)
PRINT #book_id
BEGIN
DELETE FROM "books-topics" WHERE book_id=#book_id
DELETE FROM "books-genres" WHERE book_id=#book_id
DELETE FROM books WHERE id=#book_id
END
END;
So, what I want to achieve - is to create trigger with same task,
but it must work when I delete many rows at one time, for example
DELETE FROM books WHERE id=5 OR id=3 OR id=8
by same task I mean, for example, calling the following code on each deleted row
DELETE FROM "books-topics" WHERE id=DELETEDROW.book_id
DELETE FROM "books-genres" WHERE id=DELETEDROW.book_id
DELETE FROM books WHERE id=DELETEDROW.book_id

Answer 1

Your teacher should have thought about a better example for an instead of delete trigger. This problem is what on delete cascade is there for in the first place.
However, since your assignment is to use a trigger, I would suggest something like this instead:
CREATE TRIGGER onBookDelete ON books
INSTEAD OF DELETE
AS
BEGIN
SET NOCOUNT ON;
BEGIN TRASACTION
BEGIN TRY
DELETE bt
FROM "books-topics" bt
INNER JOIN deleted d ON bt.book_id= d.book_id
DELETE bg
FROM "books-genres" bg
INNER JOIN deleted d ON bg.book_id= d.book_id
DELETE b
FROM books b
INNER JOIN deleted d ON b.book_id= d.book_id
COMMIT TRANSACTION
END TRY
BEGIN CATCH
IF ##TRANCOUNT > 0
ROLLBACK TRANSACTION
END CATCH
END;