分組多列

Question

我有以下查詢：

SELECT od.product_id, od.product_name, od.product_quantity, od.product_price, 
     o.id_address_delivery, a.id_country, a.id_state, s.name 
FROM `ps_order_detail` od 
LEFT JOIN ps_orders AS o ON od.`id_order` = o.`id_order` 
LEFT JOIN `ps_address` AS a ON o.`id_address_delivery` = a.`id_address` 
LEFT JOIN `ps_state` AS s ON a.id_state = s.id_state 
ORDER BY o.`date_add` DESC 
LIMIT 100; 

凡返回類似以下數據：

PRODUCT_ID | product_name | product_qty | product_price | id_state

我想知道在每個州的最暢銷產品（數量方面）。例如：

狀態A：最好的賣方產品A（500出售的量） 狀態B：最暢銷的是產品C（150出售量） 狀態C：最好的賣方產品A（100出售的量）

目前我正在考慮做2列之間的JOIN，但第二個想到這需要像功能「樞軸」。

我知道如何獲得合計賣出數量爲每種產品

SELECT od.product_id, od.product_name, COUNT(od.product_id) AS 'total' 
FROM `ps_order_detail` od 
GROUP BY od.product_id 
ORDER BY od.product_id DESC 
LIMIT 100; 

我也知道賣量爲每個州總，但我不知道如何既結合才達到我需要什麼。我會很感激任何幫助。謝謝

Answer 1

您需要聚合查詢的最大分組數。你可以這樣做，例如像這樣：

select state, product_name, quantity 
from (
    select id_state, state, product_id, product_name, quantity, 
    @grprow := (case when @grp = id_state then @grprow + 1 else 1 end) as grprow, 
    @grp := id_state 
    from ( 
    SELECT a.id_state, max(s.name) as state, od.product_id, 
     max(od.product_name) as product_name, 
     sum(od.product_quantity) as quantity 
    FROM `ps_order_detail` od 
    LEFT JOIN ps_orders AS o ON od.`id_order` = o.`id_order` 
    LEFT JOIN `ps_address` AS a ON o.`id_address_delivery` = a.`id_address` 
    LEFT JOIN `ps_state` AS s ON a.id_state = s.id_state 
    group by a.id_state, od.product_id 
) grped, 
    (select @grprow := 0, @grp := null) init 
    order by id_state, quantity desc, product_id 
) grpmax 
where grprow = 1 
order by id_state; 

這將總結每個狀態和產品的數量，則每個狀態的結果數，然後採取的第一個。如果兩種產品在一種狀態下具有相同的數量，則僅採用其中一種（使用較低的product_id）。如果您想同時擁有這兩個號碼，則可以調整@grprow的編號條件。