Question

我不太确定如何提出这个问题以保持它的意思，同时仍然提供足够的信息。如果任何人需要更多信息/表格让我知道，我将很乐意编辑。

我正在尝试查询数据库，需要连接几个表来获取我想要的数据。

查询是：显示供应商x中两个日期之间售出的商品数量以及当前库存中有多少商品。

这个的SQL如下：


SELECT p.id as product_id, p.description as description, SUM(col.quantity) as qty,   SUM(s.stocklevel) as stocklevel, sup.name as supplier from products as p
LEFT JOIN customerorderlines as col on col.product_id = p.id
LEFT JOIN customerorders as co on co.id = col.customerorder_id
LEFT JOIN stock as s on s.product_id = p.id
LEFT JOIN suppliers as sup on sup.id = p.supplier_id
WHERE co.orderdate BETWEEN '2009-07-01' AND '2009-08-01'
AND p.supplier_id = 51
GROUP by col.product_id
ORDER by SUM(col.quantity)
DESC

这是它重新调整的行之一：


product_id description                 qty   stocklevel  supplier
24376      Streaker Wax Paper Strips   330   3510        Rand Rocket Ltd

注意stocklevel返回3510。

现在让我们自己看一下：


SELECT SUM(stocklevel) from stock where product_id = 24376

SUM(stocklevel)
90

凭借我有限的mysql知识，我不知道为什么会这样做。任何建议都非常感激。

提前致谢。

Answer 1

您最有可能多次计算几个product_id的库存水平。

一种解决方案是预先计算每个product_id的stocklevel，并将其与原始查询结合起来。

SELECT    p.id as product_id
          , p.description as description
          , SUM(col.quantity) as qty
          , sl.stocklevel as stocklevel
          , sup.name as supplier 
from      products as p 
          INNER JOIN (
            SELECT    product_id, SUM(stocklevel) as stocklevel
            from      stock 
            GROUP BY  product_id
          ) sl ON sl.product_id = p.product_id
          LEFT JOIN customerorderlines as col on col.product_id = p.id 
          LEFT JOIN customerorders as co on co.id = col.customerorder_id 
          LEFT JOIN stock as s on s.product_id = p.id 
          LEFT JOIN suppliers as sup on sup.id = p.supplier_id 
WHERE     co.orderdate BETWEEN '2009-07-01' AND '2009-08-01' 
          AND p.supplier_id = 51 
GROUP by  col.product_id, sl.stocklevel
ORDER by  SUM(col.quantity) DESC

Answer 2

SELECT prod.id as product_id, prod.description as description, 
 SUM(col.quantity) as qty, SUM(sup.stocklevel) as stocklevel, 
 sup.name as supplier, sup.id
 FROM product prod
 INNER join suppliers sup as sup.id = prod.supplier_id
 LEFT join stock stk as stk.product_id = prod.id
 LEFT JOIN customerorderlines as col on col.product_id = prod.id
 LEFT JOIN customerorders as co on co.id = col.customerorder_id
 WHERE co.orderdate BETWEEN '2009-07-01' AND '2009-08-01'
 GROUP BY sup.id, prod.id
 ORDER by SUM(col.quantity) DESC

MYSQL JOIN返回的结果多于应有的结果

2 个答案: