Question

Any idea how to get test_trigger working?

Create table test (
    book_id Int UNSIGNED NOT NULL,
    book_views Int UNSIGNED NOT NULL DEFAULT 0,
Primary Key (book_id)) ENGINE = InnoDB;

Create table trigger_test (
    book_id Int UNSIGNED NOT NULL,
    book_views Int UNSIGNED NOT NULL DEFAULT 0,
Primary Key (book_id)) ENGINE = Memory;

delimiter $$
CREATE TRIGGER test_trigger
   AFTER UPDATE ON test
   FOR EACH ROW
   BEGIN
     DECLARE rows_count INT;
     SELECT count(1) FROM trigger_test WHERE book_id=NEW.book_id INTO @rows_count;

     IF @rows_count = 0 THEN
         INSERT INTO trigger_test(book_id, book_views)
         SELECT book_id, book_views FROM test where book_id = NEW.book_id;
     ELSE
         UPDATE trigger_test
         SET book_views = NEW.book_views
         WHERE book_id = NEW.book_id;
     END IF;
   END$$
delimiter ;

Insert/update is not working. Following code should insert row in trigger_test but its not inserting row.

insert into test values (1, 10);

Answer 1

There is no need to reference the table ‘test’. Just use the NEW table like this

INSERT INTO trigger_test(book_id,book_views)
VALUES (NEW.book_id,NEW.book_views); 

Also you could use the Replace statement.

MySQL Replace Syntax

REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted.