DB2触发器以避免重复

Question

我是DB2的新手。我有一个类似的任务，我必须编写一个触发器，在插入数据时应避免重复。

Table : Books 
Columns : book_id, book_name, author, copies

写下这样的触发器：

CREATE OR REPLACE TRIGGER tri_books_edit 
BEFORE INSERT ON books 
REFERENCING NEW AS N
FOR EACH ROW 
WHEN ((select count(*) from books where book_name = N.book_name and author = N.Author) > 0)
SIGNAL SQLSTATE '75000' SET MESSAGE_TEXT = 'Duplicate row with same name and author'

但是，它只是发送错误但我的任务是插入数据，如果书名和作者不在DB中，否则不应该插入