MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

create table t_object(Object_ID int, Name varchar(50))
create table t_operation(OperationID int, Object_ID int,  Name varchar(50))
create table t_operationtag(PropertyID int, ElementID int, Property varchar(50), VALUE varchar(50))
INSERT INTO t_object(Object_ID,Name)
VALUES
   (1,'myClass1'),
   (2,'myClass2'),
   (3,'myClass3');
INSERT INTO t_operation(OperationID, Object_ID,Name)
VALUES
   (1,1,'class1Operation1'),
   (2,1,'class1Operation2'),
   (3,1,'class1Operation3'),
   (4,2,'class2Operation1'),
   (5,2,'class2Operation2'),
   (6,2,'class2Operation3'),
   (7,3,'class3Operation1'),
   (8,3,'class3Operation2'),
   (9,3,'class3Operation3');
INSERT INTO t_operationtag(PropertyID,ElementID,Property,VALUE)
VALUES
   (1,1,'Calls','class2Operation1,class2Operation2,class2Operation3'),
   (2,2,'Calls','class3Operation1'),
   (3,3,'Calls','class3Operation2'),
   (4,4,'Calls','class3Operation3'),
   (5,5,'Calls','class1Operation1'),
   (6,6,'Calls','class1Operation2,class1Operation3'),
   (7,7,'Calls','class1Operation1,class2Operation1,class3Operation1'),
   (8,8,'Calls','None'),
   (9,9,'Calls','class2Operation1');
select t2.name, group_concat(t1.name) 
from t_operation t1
left join 
(SELECT to3.ElementID, to2.name
FROM t_object to1
left join t_operation to2 on to1.Object_ID = to2.Object_ID
left join t_operationtag to3 on find_in_set(to2.Name, to3.VALUE)
WHERE to3.Property = 'Calls'
and to1.Object_ID = '1') t2
on t1.OperationID = t2.ElementID
where t2.ElementID is not null
group by t2.name;


name
group_concat(t1.name)


class1Operation1
class2Operation2,class3Operation1

class1Operation2
class2Operation3

class1Operation3
class2Operation3

name	group_concat(t1.name)
class1Operation1	class2Operation2,class3Operation1
class1Operation2	class2Operation3
class1Operation3	class2Operation3