從具有相同列的多個表中選擇sum（）

Question

我有一個產品表，sales_item和具有以下結構的庫存

產品表：

+----+-----+-------------+
| id |name |description  |
+----+-----+-------------+
| 1  |Pr1  |prod1        |
+----+-----+-------------+
| 2  |Pr2  |prod2        |
+----+-----+-------------+
| .. |...  |.....        |
+----+-----+-------------+

sales_item_details表

+-----+----------+------------+-----+
| id  | sales_id | product_id | qty |
+-----+----------+------------+-----+
| 517 |      211 |          1 | 200 |
+-----+----------+------------+-----+
| 518 |      211 |          1 | 120 |
+-----+----------+------------+-----+

和生產

+----+------------+-------+
| id | product_id | qty   |
+----+------------+-------+
|  1 |          1 |    20 |
|  2 |          2 |   200 |
|  3 |          1 |    20 |
|  4 |          3 |    30 |
|  5 |          9 |    30 |
|  6 |         65 |    10 |
|  7 |         65 |    50 |
|  8 |         71 |    10 |
|  9 |         71 |    10 |
| 10 |         71 |    10 |
+----+------------+-------+

現在我要創建具有相同表定義的多個數據庫，並且需要維護庫存

生產表和產品表將從單個數據庫維護，僅sales_item_details表將不同，但產品ID相同

那么如何查詢以獲取銷售商品明細的SUM（qty）並查看庫存

我已經試過了：

SELECT
        `pr`.`id`,
        `pr`.`name`,
        sl.size,
        IFNULL(SUM(s.qty), 0) AS sales,
        IFNULL((SELECT SUM(qty) FROM production st WHERE st.product_id = `pr`.`product-id`), 0) AS stock_added
    FROM products pr
        LEFT JOIN (
            SELECT qty, product_id FROM db1.sales_item_details
            UNION ALL 
            SELECT qty, product_id FROM db2.sales_item_details 
        ) s ON pr.`id` = s.product_id
        LEFT JOIN size_list sl ON sl.id = `pr`.`product-size`
    GROUP BY s.product_id
    ORDER BY sales DESC

但是得到出售的產品

任何幫助將被申請

Answer 1

首先，我在主數據庫中創建了一個視圖，其中包含按產品ID分組的所有銷售項目：

CREATE OR REPLACE VIEW unit_sold_all  AS
    SELECT 
        p.`product-id` AS product_id,
        (
            (SELECT IFNULL(SUM(s0.qty), 0) FROM db_1.sales_item_details s0 WHERE s0.product_id = p.`product-id`) + 
            (SELECT IFNULL(SUM(s1.qty), 0) FROM db_2.sales_item_details s1 WHERE s1.product_id = p.`product-id`) + 
            (SELECT IFNULL(SUM(s2.qty), 0) FROM db_3.sales_item_details s2 WHERE s2.product_id = p.`product-id`) + 
            (SELECT IFNULL(SUM(s3.qty), 0) FROM db_4.sales_item_details s3 WHERE s3.product_id = p.`product-id`) + 
            (SELECT IFNULL(SUM(s4.qty), 0) FROM db_5.sales_item_details s4 WHERE s4.product_id = p.`product-id`) 
        ) as total_unit_sales
FROM products p

然后在另一個sql中，我選擇了銷售額的總和。

PS：我本人回答了這個問題，因為將來其他人可能需要這樣做。