MySQL 8.0

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CREATE TABLE batch 
    (`batch_no` int)
;
    
INSERT INTO batch 
    (`batch_no`)
VALUES
    (1),
    (2),
    (3),
    (4),
    (5),
    (6),
    (9),
    (10),
    (12)
;
CREATE TABLE subbatch (
  `batch_no` INTEGER,
  `subbatch_no` INTEGER
);

INSERT INTO subbatch
  (`batch_no`, `subbatch_no`)
VALUES
  ('7', '1'),
  ('7', '2'),
  ('7', '3'),
  ('8', '1'),
  ('8', '2'),
  ('11', '1'),
  ('11', '2');
SELECT CAST(batch_no as char) batchno FROM batch 
UNION 
SELECT CONCAT(batch_no,'-',subbatch_no) FROM subbatch 
ORDER BY batchno+0 ASC


batchno


1

2

3

4

5

6

7-1

7-2

7-3

8-1

8-2

9

10

11-1

11-2

12