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我有我试图执行一个查询的以下三个表：MySQL的GROUP BY和限制加入
订单
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
凭证是在订单中购买的，然后将此订单的ID保存到凭证以保存购买时间的记录。
在以后的日期，可以使用凭证以其他订单购买商品。每张凭证都有现金价值，因此可以按多个订单使用，直到其价值完全用完为止。
我试图想出一个查询，它将按购买的年份和月份对购买凭证进行分组，并显示有多少人被购买，并且在他们第一次使用之前已经花了多少时间，最多用了12个月。
这是我到目前为止有：
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)
这正确地计算所购买的凭证，如果他们没有被然而，一旦他们开始习惯于使用时，外部联接导致凭证多次计算。此外，它还计算每次使用优惠券的时间，当我只想要第一次使用时。
任何人都可以帮忙吗？
任何意见赞赏。
谢谢。