Child, parent table

SQL
1

Hello,

I am wondering in MySQL how can we know which table is a parent and which is a child?
thanks

2

Hi.
Typically the child table is the one having the foreign keys to their related parent.
So as far as I am concerned this is what I would rely on to tell.

Regards.

Sample code to play with

DROP DATABASE IF EXISTS test;
CREATE DATABASE IF NOT EXISTS test;

DROP TABLE IF EXISTS test.child;
DROP TABLE IF EXISTS test.parent;

CREATE TABLE IF NOT EXISTS test.parent (
    parent_id INT AUTO_INCREMENT PRIMARY KEY,
    parent_data_1 VARCHAR(10) UNIQUE NOT NULL,
    parent_data_2 DECIMAL(7 , 2 ) CHECK ((parent_data_2 <> NULL)
        AND (parent_data_2 BETWEEN 50.01 AND 99.99)),
    parent_data_3 ENUM('Y', 'N', 'U')
)  ENGINE=INNODB;

CREATE TABLE IF NOT EXISTS test.child (
    child_id INT PRIMARY KEY AUTO_INCREMENT,
    child_data VARCHAR(20) UNIQUE NOT NULL,
    parent_id INT,
    CONSTRAINT FK_Child_Parent 
		FOREIGN KEY (parent_id)
        REFERENCES parent (parent_id)
        ON DELETE CASCADE
        ON UPDATE NO ACTION
)  ENGINE=INNODB;

INSERT INTO test.child (child_data) 
VALUES 
('Lorem'),
('Ipsum'),
('and'),
('some'),
('more');

-- There is no Parent with ID 1000 and fails
-- Comment if needs be
-- INSERT INTO test.child (child_data, parent_id) 
-- VALUES ('test',1000);

-- Lets insert a valid parent
INSERT INTO test.parent (parent_data_1)
VALUES ('p data 1'),('p data 2');

INSERT INTO test.parent (parent_data_1, parent_data_2)
VALUES ('p data 3',50.1),('p data 4',99.99);

-- This will run
INSERT INTO test.child (child_data, parent_id) 
VALUES 
('test 1',4),
('test 2',3),
('test 3',2),
('test 4',1),
('test 5',2),
('test 6',3),
('test 7',4);

SELECT 
    p.*, c.*
FROM
    test.parent AS p
        INNER JOIN
    test.child AS c ON p.parent_id = c.parent_id
ORDER BY child_data DESC;