Question

我希望看到客户从特定制造商那里订购了什么产品。

我有这些表（带列）：

项目（item_num， order_num ，stock_num， manu_code ，数量等）
股票（stock_num， manu_code ，描述，unit_price等）
订单（ order_num ，order_date， customer_num ，ship_instruct等）
客户（ customer_num ，fname，lname，company，address1等）

这是我现在的查询，但我相信它会返回某种类型的交叉产品：

SELECT concat(c.fname," ", c.lname) AS fullname, s.description
FROM items i, stock s, customer c JOIN orders o 
ON o.customer_num=c.customer_num 
WHERE o.order_num=i.order_num AND i.manu_code = 'ANZ';

返回一个包含大量重复内容的大型列表（1000行），

Anthony Higgens | baseball gloves
Anthony Higgens | baseball gloves
       .                 .
       .                 .
       .                 .
Kim Satifer     | running shoes

我做错了什么？

Answer 1

FROM items i, stock s, customer c对所涉及的这三个表进行了笛卡尔联合，但您的WHERE对该笛卡尔联接的限制很少。

如果你做了一些更明确的加入，你将会仔细减少重复，并更恰当地表达你想要做的事情。使用INNER JOINS和正确的加入条件，而不是仅列出FROM之后的所有表格。示例:(有更多此类条件，您需要应用于JOINS，但这是一个示例）：INNER JOIN stock ON stack.manu_code = items.manu_code。

最后，您可以使用SELECT DISTINCT或GROUP BY来进一步减少重复项。但是，如果你明确JOIN的JOIN标准是正确的，那么你不应该有太多的重复。

Answer 2

试试这个：

SELECT DISTINCT concat(c.fname," ", c.lname) AS fullname, s.description
FROM customer c 
INNER JOIN orders o ON c.customer_num = o.customer_num
INNER JOIN items i ON o.order_num = i.order_num
INNER JOIN stock s on s.stock_num = i.stock_num
WHERE i.manu_code = 'ANZ'

Answer 3

这应该有效：


        SELECT          concat(a.fname, " ", a.lname ) as name
                        , d.description as desc
        FROM            CUSTOMER    a
        INNER JOIN      ORDERS      b
            on          a.customer_num = b.customer_num
        INNER JOIN      ITEMS       c
            on          b.order_num = c.order_num
        INNER JOIN      STOCK       d
            on          c.manu_code = d.manu_code
        where           c.manu_code like 'ANZ'
        group by        name,desc

Answer 4

谢谢大家，我认为现在正在运作：

SELECT DISTINCT concat(c.fname," ", c.lname) AS fullname, s.description
FROM customer c 
INNER JOIN orders o ON c.customer_num = o.customer_num
INNER JOIN items i ON o.order_num = i.order_num
INNER JOIN stock s on s.stock_num = i.stock_num
WHERE i.manu_code = 'ANZ';

如何在MySQL中连接多个表？

4 个答案: