与多个嵌套选择的左联接

Question

以下语句出人意料地起作用，但是我不确定3次加入同一张表是否有效。 我必须禁用ONLY_FULL_GROUP_BY才能使其正常运行。

有2张桌子在玩。 一个是包含Distributor信息的主表，第二个是包含主表（assoc）中关联的Distributor的amount ， date和id的购买表。

我需要三件事。 年初至今的销售额，该总额表示某个分销商从当年起的销售额。 去年的销售额，与上一年相同。 然后，最后只需获取最新的购买日期和金额即可。

用户需要能够按这些值（ lys ， ytd等）进行过滤，因此将它们作为变量连接似乎是一种方法。 数据库大小约为7,000条记录。

SELECT 
    d.*,
    ytd_total,
    lys_total,
    last_amount,
    last_purchase

FROM Distributor as d
LEFT JOIN (
    SELECT
        assoc, SUM(amount) ytd_total
        FROM purchases
        WHERE db = 1 AND purchase_date >= '{$year}-01-01'
        GROUP BY assoc
) AS ytd
ON ytd.assoc = d.id

LEFT JOIN (
    SELECT
        assoc, SUM(amount) lys_total
        FROM purchases
        WHERE db = 1 AND purchase_date BETWEEN '{$lyear}-01-01' AND '{$lyear}-12-31'
        GROUP BY assoc
) AS lys
ON lys.assoc = d.id

LEFT JOIN (
    SELECT
        assoc, amount last_amount, purchase_date last_purchase
        FROM purchases
        WHERE db = 1
        GROUP BY assoc
) AS lst
ON lst.assoc = d.id

WHERE ........

Answer 1

您可以在每个聚合查询中做更多的工作。 我认为这更是您想要的：

select d.*, pa.ytd_total, pa.lys_total, pa.last_purchase_date, p.amount
from distributor d left join
     (select p.assoc,
             sum(case when p.purchase_date >= '{$year}-01-01' then p.amount end) as ytd_total,
             sum(case when p.purchase_date BETWEEN '{$lyear}-01-01' AND '{$lyear}-12-31' then p.amount end) as lys_total,
             max(p.purchase_date) as last_purchase_date             
      from purchases p
      where p.db = 1
      group by p.assoc
     ) pa left join
     purchases p
     on pa.assoc = p.assoc and pa.last_purchase_date = p.purchase_date;