MySql Define foreign key with multiple columns throws error - mysql

Question

I have 2 tables. And queries are below.
CREATE TABLE `queue_service_settings` (
`app_id` int(11) NOT NULL,
`app_id_type` int(11) NOT NULL,
`channel_id` int(11) NOT NULL,
`setting_type` varchar(255) NOT NULL,
`setting_key` varchar(255) NOT NULL,
`setting_value` varchar(255) NOT NULL,
`update_time` datetime DEFAULT CURRENT_TIMESTAMP,
`create_time` datetime DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (app_id,app_id_type),
KEY `index_qss_app_id` (`app_id`) USING BTREE,
KEY `index_qss_setting_type` (`setting_type`) USING BTREE,
KEY `index_qss_setting_key` (`setting_key`) USING BTREE,
KEY `index_qss_channel_id` (`channel_id`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `queue_applications` (
`app_id` int(11) NOT NULL,
`app_id_type` int(11) NOT NULL,
`channel_id` int(11) NOT NULL,
`app_name` varchar(255) NOT NULL,
`callback_url` varchar(255) NOT NULL,
`update_time` datetime DEFAULT CURRENT_TIMESTAMP,
`create_time` datetime DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`app_id`,`app_id_type`,`channel_id`),
KEY `fk_qa_channel_id` (`channel_id`),
CONSTRAINT `fk_qa_app_id_app_id_type_channel_id` FOREIGN KEY (app_id,app_id_type,channel_id) REFERENCES queue_service_settings(app_id,app_id_type,channel_id)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
And i am getting this error
Cannot add foreign key constraint Create table
'event_processor_test/queue_applications' with foreign key constraint
failed. There is no index in the referenced table where the referenced
columns appear as the first columns.
When i tried to define this 3 columns (app_id,app_id_type,channel_id) as primary key its ok but primary key should be just (app_id,app_id_type)

Answer 1

The columns in the foreign key must match the columns of the primary key referenced in the other table. You have two columns in the primary key of queue_service_settings, so you should have two columns in the foreign key that references it.
CREATE TABLE `queue_applications` (
`app_id` int(11) NOT NULL,
`app_id_type` int(11) NOT NULL,
`channel_id` int(11) NOT NULL,
`app_name` varchar(255) NOT NULL,
`callback_url` varchar(255) NOT NULL,
`update_time` datetime DEFAULT CURRENT_TIMESTAMP,
`create_time` datetime DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`app_id`,`app_id_type`,`channel_id`),
KEY `fk_qa_channel_id` (`channel_id`),
CONSTRAINT `fk_qa_app_id_app_id_type_channel_id`
FOREIGN KEY (app_id,app_id_type)
REFERENCES queue_service_settings(app_id,app_id_type)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;