MySQL 5.6

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
select version();


version()


5.6.48


CREATE TABLE `card_data` (
    `data_id` INT(11) NOT NULL AUTO_INCREMENT,
    `data` TEXT NULL DEFAULT NULL COLLATE 'utf8_general_ci',
    PRIMARY KEY (`data_id`) USING BTREE
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
AUTO_INCREMENT=51
;
INSERT INTO card_data 
VALUES (21, '{R}'), (3, '{3}');
SELECT * FROM card_data;


data_id
data


3
{3}

21
{R}


CREATE TABLE `card_data_link` (
    `card_id` INT(11) NULL DEFAULT NULL,
    `data_id` INT(11) NULL DEFAULT NULL,
    INDEX `card_id` (`card_id`) USING BTREE,
    INDEX `data_id` (`data_id`) USING BTREE,
    CONSTRAINT cdl_cd_fk FOREIGN KEY (data_id) REFERENCES card_data (data_id)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
;
INSERT INTO card_data_link 
VALUES
(63, 21),
(34, 3),
(34, 21),
(34, 21);
SELECT * FROM card_data_link;


card_id
data_id


63
21

34
3

34
21

34
21


SELECT * FROM card_data;


data_id
data


3
{3}

21
{R}


select 
    COUNT(*) AS the_cnt,
    cdl.card_id,
    cdl.data_id,
    cd.data
from
    card_data_link cdl
left join
    card_data cd on cd.data_id = cdl.data_id
GROUP BY cdl.card_id, cdl.data_id
ORDER BY card_id, data_id;


the_cnt
card_id
data_id
data


1
34
3
{3}

2
34
21
{R}

1
63
21
{R}