SELECT DISTINCT email FROM `jm_order`

sam@gmail.com
josh@gmail.com
Sam@gmail.com
john@gmail.com

SELECT DISTINCT UPPER(email) FROM `jm_order`

SELECT DISTINCT LOWER(email) FROM `jm_order`

select email
from jm_order
group by lower(email);

SELECT DISTINCT LOWER(email) AS email
FROM `jm_order`