MySQL 8.0

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CREATE TABLE Parent
(id INT,title VARCHAR(50));

INSERT INTO Parent VALUES
(1,'A'),
(2,'B'),
(3,'C');

CREATE TABLE Childs
(id INT, p_id INT, number INT);

INSERT INTO Childs VALUES
(1,1,1),(2,1,2),(3,1,3),
(4,2,4),(5,2,5),(6,2,6),
(7,3,2),(8,3,7),(9,3,8),(10,3,9);

Records: 3  Duplicates: 0  Warnings: 0



Records: 10  Duplicates: 0  Warnings: 0


SELECT p.id, p.title, GROUP_CONCAT(number ORDER BY number) val
FROM Parent p JOIN Childs c ON p.id=c.p_id
GROUP BY p.id, p.title
HAVING SUBSTRING_INDEX(val,',',1) > 3;


id
title
val


2
B
4,5,6


/*without HAVING clause*/
SELECT p.id, p.title, GROUP_CONCAT(number ORDER BY number) val
FROM Parent p JOIN Childs c ON p.id=c.p_id
GROUP BY p.id, p.title;


id
title
val


1
A
1,2,3

2
B
4,5,6

3
C
2,7,8,9