从MySQL date_format中的%m和%d中删除前导零

您可以使用%c格式化没有前导零的月份并%e格式化月份的日期:

SELECT   DATE_FORMAT(earning_created, '%Y, %c, %e') AS day, -- Here! 
         SUM(earning_amount) AS amount
FROM     earnings
WHERE    earning_account_id = ?
GROUP BY DATE(earning_created)
ORDER BY earning_created