MySQL 5.7

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CREATE TABLE work1
(
wo int (5),
duration int (5));
insert into work1 values 
( 1 ,30),
( 2 ,45),
( 3 ,30),
( 4 ,40),
( 5 ,60),
( 6 ,80),
( 7 ,11);
CREATE TABLE part1
(
part VARCHAR (5),
wo int (5));
insert into part1 values 
("A" ,1),
('A' ,2),
('A' ,3),
('A' ,4),
('A' ,5),
('B' ,6),
('B' ,7),
('C' ,8),
('C' ,9),
('D' ,10);
SELECT w1.wo,
       p2.part,
       w1.duration
       FROM (SELECT p1.part
                    FROM part1 p1
                    GROUP BY p1.part
                    ORDER BY count(*) DESC
                    LIMIT 1) x
            INNER JOIN part1 p2
                       ON p2.part = x.part
            INNER JOIN work1 w1
                       ON w1.wo = p2.wo;


wo
part
duration


1
A
30

2
A
45

3
A
30

4
A
40

5
A
60