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我有我試圖執行一個查詢的以下三個表：MySQL的GROUP BY和限制加入
訂單
id
created_at
券
id
order_id
initial_value
current_value
vouchers_used_in_orders
voucher_id
order_id
amount_used
value_before
value_after
憑證是在訂單中購買的，然後將此訂單的ID保存到憑證以保存購買時間的記錄。
在以後的日期，可以使用憑證以其他訂單購買商品。每張憑證都有現金價值，因此可以按多個訂單使用，直到其價值完全用完爲止。
我試圖想出一個查詢，它將按購買的年份和月份對購買憑證進行分組，並顯示有多少人被購買，並且在他們第一次使用之前已經花了多少時間，最多用了12個月。
這是我到目前爲止有：
SELECT
YEAR(o.created_at) AS year_purchased,
MONTH(o.created_at) AS month_purchased,
SUM(IF(v.current_value = v.initial_value, 1, 1)) AS number_sold,
SUM(IF(v.current_value = v.initial_value, 0, 1)) AS number_used,
SUM(IF(v.current_value = v.initial_value, 1, 0)) AS number_not_used,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at) AND MONTH(vuo.created_at) = (MONTH(o.created_at)), 1, 0)) AS number_used_month_0,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 1 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 1 MONTH)), 1, 0)) AS number_used_month_1,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 2 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 2 MONTH)), 1, 0)) AS number_used_month_2,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 3 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 3 MONTH)), 1, 0)) AS number_used_month_3,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 4 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 4 MONTH)), 1, 0)) AS number_used_month_4,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 5 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 5 MONTH)), 1, 0)) AS number_used_month_5,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 6 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 6 MONTH)), 1, 0)) AS number_used_month_6,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 7 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 7 MONTH)), 1, 0)) AS number_used_month_7,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 8 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 8 MONTH)), 1, 0)) AS number_used_month_8,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 9 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 9 MONTH)), 1, 0)) AS number_used_month_9,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 10 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 10 MONTH)), 1, 0)) AS number_used_month_10,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 11 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 11 MONTH)), 1, 0)) AS number_used_month_11,
SUM(IF(YEAR(vuo.created_at) = YEAR(o.created_at + INTERVAL 12 MONTH) AND MONTH(vuo.created_at) = (MONTH(o.created_at + INTERVAL 12 MONTH)), 1, 0)) AS number_used_month_12
FROM vouchers v
INNER JOIN orders o
ON o.id = v.order_id
LEFT OUTER JOIN vouchers_used_in_orders vu
ON vu.voucher_id = v.id
LEFT OUTER JOIN orders vuo
ON vuo.id = vu.id
GROUP BY
YEAR(o.created_at), MONTH(o.created_at)
ORDER BY
YEAR(o.created_at), MONTH(o.created_at)
這正確地計算所購買的憑證，如果他們沒有被然而，一旦他們開始習慣於使用時，外部聯接導致憑證多次計算。此外，它還計算每次使用優惠券的時間，當我只想要第一次使用時。
任何人都可以幫忙嗎？
任何意見讚賞。
謝謝。