如何在mysql中使用內部連接從一張表中獲取總和

Question

我有兩個表，一個是訂單，第二個是 order_product，我必須在其中使用買家 ID 找出與客戶對應的訂單數、產品數、總金額，我已成功從中找出訂單數和產品數，但我的總金額不是來對了。

訂單：

.......................................
 order_id   or_buyer_id   or_total_amt
.......................................
    1           21           10
    2           22           10
    3           21           10

訂單_產品

.................................
op_id  op_order_id  op_buyer_id
.................................
  1       1          21
  2       1          21
  3       2          22
  4       3          21

我想要低於輸出，但我的 totalamount 值出錯了，它是 30，但正確的值是 20，我在下面的正確輸出中提到過。

我想要的輸出：

............................................
or_buyer_id  orders  product   totalmount
...........................................
   21         2       3          20
   22         1       1          10

我已經嘗試了下面的查詢，它給出了 30 的 totalamount 值，這是錯誤的。

SELECT o.or_buyer_id
     , count(DISTINCT o.order_id) as orders
     , count(op.op_id) as product
     , SUM(o.or_total_amt) as totalamount 
  FROM orders as o
  JOIN order_product as op 
    on op.op_order_id = o.order_id 
   and o.or_buyer_id = op.op_buyer_id 
 group 
    by o.or_buyer_id

Answer 1

一種方法是從子查詢中的order_product表中刪除重復的行。 然后，像您已經在做的那樣將其加入orders 。 這里的一個小技巧是，在刪除子查詢中的重復項時，我們保持order_product表中原始記錄的數量。 這是因為product列反映了真實的原始記錄數。 但是totalamount不反映重復項，因此我們將該數量與刪除重復項相加。

SELECT
    t1.op_buyer_id,
    COUNT(DISTINCT t1.op_order_id) AS orders,
    SUM(t1.cnt) AS product,
    SUM(t2.or_total_amt) AS totalamount
FROM
(
    SELECT op_order_id, op_buyer_id, COUNT(*) AS cnt
    FROM order_product
    GROUP BY op_order_id, op_buyer_id
) t1
INNER JOIN orders t2
    ON t1.op_order_id = t2.order_id AND
       t1.op_buyer_id = t2.or_buyer_id
GROUP BY
    t1.op_buyer_id
ORDER BY
    t1.op_buyer_id;

演示

Answer 2

您應該在內連接中使用子查詢，而不是直接引用 order_product 表：

嘗試用 order_product 替換

(SELECT DISTINCT op_order_id, op_buyer_id
 FROM order_product) AS op

這將刪除給您錯誤總和的重復項。

我還引入了一個子查詢來獲取正確的產品值：

SELECT count(op_order_id) FROM order_product WHERE order_id = o.order_id AND op_buyer_id = o.or_buyer_id) as product

最終的 SQL 是：

SELECT o.`or_buyer_id`, 
       count(DISTINCT o.`order_id`) as orders, 
       (SELECT count(op_order_id) FROM order_product WHERE order_id = o.order_id AND op_buyer_id = o.or_buyer_id) as product,
       SUM(o.`or_total_amt`) as totalamount 
FROM `orders` as o 
INNER JOIN (SELECT DISTINCT op_order_id, 
                            op_buyer_id
            FROM order_product) AS op 
ON op.op_order_id=o.order_id AND o.or_buyer_id = op.op_buyer_id 
GROUP BY o.`or_buyer_id`

Answer 3

你應該使用這個子查詢

SELECT tbl.op_buyer_id, COUNT(DISTINCT tbl.op_order_id) AS orders, SUM(tbl.cont) AS product, SUM(tbl2.or_total_amt) AS totalamount FROM ( SELECT op_order_id, op_buyer_id, COUNT(*) AS cont FROM order_product GROUP BY op_order_id, op_buyer_id ) tbl INNER JOIN orders tbl2 ON tbl.op_order_id = tbl2.order_id AND tbl.op_buyer_id = tbl2.or_buyer_id GROUP BY tbl.op_buyer_id ORDER BY tbl.op_buyer_id