MySQL 5.6

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

CREATE TABLE tablename
    (`launch_month` date)
;
    
INSERT INTO tablename
    (`launch_month`)
VALUES
    ('2018-06-01'),
    ('2018-07-01'),
    ('2018-08-01')
;

Records: 3  Duplicates: 0  Warnings: 0


select launch_month, 
       left(replace(launch_month, '-', ''), 6) launch_id
from tablename


launch_month
launch_id


2018-06-01
201806

2018-07-01
201807

2018-08-01
201808


select launch_month, 
       date_format(launch_month, '%Y%m') launch_id
from tablename


launch_month
launch_id


2018-06-01
201806

2018-07-01
201807

2018-08-01
201808