Question

我在mySQL数据库上有3个表。 产品，库存入库，库存出库。我想按 product_id 对每种产品的库存量和缺货量进行总计。
我在下面使用此查询。但这给了我一些错误的答案。

SELECT product.Product_Name, SUM(stock_in.StockInQuantity) as stockin, S
        SUM(stock_out.Quantity) as stockout 
FROM product, stock_in, stock_out 
WHERE stock_in.Product_ID=product.Product_ID 
and stock_out.Product_ID=product.Product_ID 
GROUP BY product.Product_ID**

但是，如果我对stockin和stockout使用单独的查询，则结果是正确的。

SELECT Product_Name, SUM(StockInQuantity) as stockin 
FROM product, stock_in 
WHERE stock_in.Product_ID=product.Product_ID 
GROUP BY product.Product_ID


SELECT Product_Name, SUM(Quantity) as stockout 
FROM product, stock_out 
WHERE stock_out.Product_ID=product.Product_ID 
GROUP BY product.Product_ID**

因此，请给我一个解决方案，以在一个查询中查找结果或在一个表中回显两个查询结果的结果。

Answer 1

您可以尝试以下查询：

SELECT p.product_name AS Product_Name,
   COALESCE(SUM(si.stockin), 0) AS total_stockin,
   COALESCE(SUM(so.stockout), 0) AS total_stockout,
FROM product p
LEFT JOIN (SELECT Product_ID, SUM(StockInQuantity) AS stockin
       FROM stock_in 
       GROUP BY Product_ID) si ON si.Product_ID = p.Product_ID
LEFT JOIN (SELECT Product_ID, SUM(Quantity) AS stockout
       FROM stock_out 
       GROUP BY Product_ID) so ON so.Product_ID = p.Product_ID
GROUP BY Product_Name

多个表中的查询中的多个sun函数

1 个答案: