MySQL 5.7

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CREATE TABLE TableB (
  `id` INTEGER,
  `working_date` DATE
);

INSERT INTO TableB
  (`id`, `working_date`)
VALUES
  ('1', '2020-08-01'),
  ('2', '2020-08-02'),
  ('3', '2020-08-03');

CREATE TABLE TableA (
  `id` INTEGER,
  `name` VARCHAR(6),
  `working_date` DATETIME
);

INSERT INTO TableA
  (`id`, `name`, `working_date`)
VALUES
  ('1', 'king', '2020-08-01'),
  ('2', 'king', '2020-08-02'),
  ('3', 'queen', '2020-08-01'),
  ('4', 'queen', '2020-08-02'),
  ('5', 'rook', '2020-08-03'),
  ('6', 'bishop', '2020-08-01'),
  ('7', 'bishop', '2020-08-01'),
  ('8', 'queen', '2020-08-03');
select n.name, b.working_date missing_date 
from TableB b
cross join (select distinct name from TableA) n
left join TableA a on a.name = n.name and a.working_date = b.working_date
where a.id is null


name
missing_date


king
2020-08-03

rook
2020-08-01

rook
2020-08-02

bishop
2020-08-02

bishop
2020-08-03


select n.name, count(*) missing_dates 
from TableB b
cross join (select distinct name from TableA) n
left join TableA a on a.name = n.name and a.working_date = b.working_date
where a.id is null
group by n.name


name
missing_dates


bishop
2

king
1

rook
2

name	missing_date
king	2020-08-03
rook	2020-08-01
rook	2020-08-02
bishop	2020-08-02
bishop	2020-08-03