SELECT
client_payment_amount.RECEIPT_NO,
Count(classroom_book.ID) AS CLASS_PER_MONTH,
classroom_book.GROUP_ID,
YEAR(classroom_book.DATE),
MONTH(classroom_book.DATE)
FROM
client_payment_amount
LEFT JOIN client ON client_payment_amount.CLIENT_ID = client.ID
LEFT JOIN group_register ON group_register.CLIENT_ID = client.ID
LEFT JOIN classroom_book ON classroom_book.GROUP_ID = group_register.GROUP_ID
GROUP BY
classroom_book.GROUP_ID,
YEAR(classroom_book.DATE),
MONTH(classroom_book.DATE)
ORDER BY
client_payment_amount.RECEIPT_NO,
classroom_book.DATE