MySql composite foreign key ON DELETE set null [duplicate] - mysql

Question

This question already has an answer here:
Multiple Column Foreign Key: Set single column to Null "ON DELETE" instead of all
(1 answer)
Closed 2 years ago.
Please refer to this SQLFiddle
CREATE TABLE `parent` (
`id` varchar(64) NOT NULL,
`master_id` varchar(64) NOT NULL,
`c1_id` varchar(64) DEFAULT NULL,
`c2_id` varchar(64) DEFAULT NULL,
PRIMARY KEY (`master_id`, `id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `child_1` (
`id` varchar(64) NOT NULL,
`master_id` varchar(64) NOT NULL,
PRIMARY KEY (`master_id`, `id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `child_2` (
`id` varchar(64) NOT NULL,
`master_id` varchar(64) NOT NULL,
PRIMARY KEY (`master_id`, `id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO child_1 (`id`, `master_id`)
VALUES
(1, 'm1');
INSERT INTO child_2 (`id`, `master_id`)
VALUES
(2, 'm2'),
(3, 'm1');
INSERT INTO parent (`id`, `master_id`, `c1_id`, `c2_id`)
VALUES
(4, 'm1', null, null),
(5, 'm1', 1, null),
(6, 'm2', null, 2);
I have multiple tables that have composite Primary Key.
All PK are PRIMARY KEY (master_id, id)
And now I try to add Foreign Keys to these tables.
ALTER TABLE `parent`
ADD CONSTRAINT parent_fk_1
FOREIGN KEY (`master_id`, `c1_id`)
REFERENCES child_1 (`master_id`, `id`)
ON UPDATE CASCADE
ON DELETE SET NULL;
But it throws error Cannot add foreign key constraint.
Here parent.master_id always must stay NOT NULL while c1_id and c2_id can be set to NULL.
Is it possible to achieve this kind of Foreign Key setup?
I found that there is MATCH SIMPLE option that allows composite key to be partial NULL, but how to apply it for ON DELETE SET NULL?

Answer 1

Both referring Column are NOT NULL, so you can't use ON DELETE SET NULL, this violates the NOT NULL
ALTER TABLE `parent`
ADD CONSTRAINT parent_fk_1
FOREIGN KEY (`master_id`, `c1_id`)
REFERENCES child_1 (`master_id`, `id`)
ON UPDATE CASCADE;