mysql> create database lib;
Query OK, 1 row affected (0.31 sec)
mysql> use lib;
Database changed
mysql> create table library_2
-> (id int AUTO_INCREMENT primary key,
-> Book_name varchar(20),
-> Details varchar(50));
Query OK, 0 rows affected (2.24 sec)
mysql> insert into library_2 values
-> (1,'aaa','bbb'),
-> (2,'ccc','ddd'),
-> (3,'eee','fff'),
-> (4,'ggg','hhh');
Query OK, 4 rows affected (0.46 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select*from library_2;
+----+-----------+-------------------+
| id | Book_name | Details |
+----+-----------+-------------------+
| 1 | aaa | bbb |
| 2 | ccc | ddd |
| 3 | eee | fff |
| 4 | ggg | hhh |
+----+-----------+-------------------+
4 rows in set (0.00 sec)
mysql> create table library_audit2
-> (id int AUTO_INCREMENT primary key,
-> Book_Name varchar(20) not null,
-> Details varchar(50) default null,
-> change_date date,
-> library_id int,
-> foreign key(library_id) REFERENCES library_2(id));
Query OK, 0 rows affected (2.33 sec)
mysql> insert into library_audit2 values
-> (10,'aaa','bbb','2011-9-1',1),
-> (20,'ccc','ddd','2012-8-2',2),
-> (30,'eee','fff','2013-7-3',3),
-> (40,'ggg','hhh','2014-6-4',4);
Query OK, 4 rows affected (0.20 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select*from library_audit2;
+----+-----------+---------+-------------+------------+
| id | Book_Name | Details | change_date | library_id |
+----+-----------+---------+-------------+------------+
| 10 | aaa | bbb | 2011-09-01 | 1 |
| 20 | ccc | ddd | 2012-08-02 | 2 |
| 30 | eee | fff | 2013-07-03 | 3 |
| 40 | ggg | hhh | 2014-06-04 | 4 |
+----+-----------+---------+-------------+------------+
4 rows in set (0.00 sec)
mysql> create trigger BeforeLibraryDelete1
-> BEFORE DELETE
-> ON library_audit2 FOR EACH ROW
-> BEGIN
-> declare id1 int;
-> select library_id into id1 from library_audit2 where change_date=OLD.change_date;
-> delete from library_2 li where li.id=id1;
-> END $$
Query OK, 0 rows affected (0.45 sec)
mysql> DELIMITER ;
mysql> Delete from library_audit2 where change_date='2011-09-01';
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`abc`.`library_audit2`, CONSTRAINT `library_audit2_ibfk_1` FOREIGN KEY (`library_id`) REFERENCES `library_2` (`id`))
I know what this error means, but i need a different trigger query to rectify this problem. This seems to ending up wrong no matter what I try. Kindly provide me with a query that works. Also because MYSQL doesn't work with INSTEAD OF, don't provide me with a query that has INSTEAD OF DELETE in it. But a replacement for it in MYSQL would be highly appreciated.
You are running in an endless loop.
You have a delete trigger on the table library_audit2 and in that trigger you delete from the same table which invokes another trigger and so on.
The DB won't allow that and returns that error message.