Question

    SELECT ai.auction_item_id, ai.starting_bid, b.bid_amount, i.*
    FROM
    auction_item as ai, //Table contains auction specific details about the item
    item as i //Table contains general details about the item
    INNER JOIN (
            SELECT auction_item_id, bid_amount
            FROM bid xb //Table contains bids on item
            ORDER BY amount DESC
            LIMIT 1 ) b 
     ON b.auction_item_id = ai.auction_item_id
    WHERE
    ai.auction_id = 4 AND
    i.id = ai.listings_id

    ORDER BY RAND()
    LIMIT 4

目前通过上述查询，我可以从当前有效拍卖中获得4个随机项目（拍卖＃4）。但他们目前都以相同的最高出价金额回归（来自内部联盟）。每个项目都应有自己的最高出价金额（来自内部联接） - 除非该项目没有出价，那么它应为0（或某事）

我在这里做错了什么？对于每个出价，出价表都有一行，因此LIMIT 1和内部联接中的desc按顺序排序，因为我想要对外部区域中的每个项目进行最高出价。（如果有出价）。

由于

Answer 1

尝试子查询。如果由于0而在出价表中没有条目，则会获得coalesce。

SELECT 
    ai.auction_item_id, ai.starting_bid, 
    Coalesce((SELECT max(xb.bid_amount)
              FROM bid xb
              WHERE xb.auction_item_id = ai.auction_item_id), 0) AS bid_amount,
    i.*
FROM auction_item AS ai
INNER JOIN item AS i ON i.id = ai.listings_id
WHERE ai.auction_id = 4 
ORDER BY Rand()

Answer 2

这样的东西？

SELECT ai.auction_item_id, ai.starting_bid, b.bid_amount, max(bid_amount)
    FROM auction_item as ai
      inner join bid b
        on ai.auction_item_id = b.auction_item_id
      inner join items i
        on i.id = ai.listings_id
    where ai.auction_id = 4

将表格架构添加到问题中会有所帮助

修改：

SELECT ai.auction_item_id, ai.starting_bid, IFNULL(max(bid_amount), 0) max_bid FROM auction_item as ai left join bid b on ai.auction_item_id = b.auction_item_id inner join items i on i.id = ai.listings_id WHERE ai.auction_id = 4 GROUP BY ai.auction_item_id

在这里，包括没有出价项目。

如果我有错误的话，请告诉我：http://sqlfiddle.com/#!9/0eae7/2

Answer 3

有几个问题：

根据Hockenberry，使用LIMIT 1交叉加入派生表只会重复每次最高出价，更糟糕的是，它不会被过滤，因此它将是 any <的最高出价/ em>拍卖，如果该行不适用于当前auction_item_id，则会将其加入。将LIMIT移动到外部查询。

即使没有出价，您也希望使用LEFT JOIN返回一行。

您还需要INNER JOIN auction_item到item（您的初始查询无法运行）

<德尔> SELECT ai.auction_item_id， ai.starting_bid， COALESCE（b.bid_amount，0）为bid_amount，一世。* 从auction_item作为ai 内部联接项目为我 ON i.id = ai.listings_id LEFT JOIN（ SELECT auction_item_id，bid_amount 从出价xb ORDER BY金额DESC）b ON b.auction_item_id = ai.auction_item_id 哪里 ai.auction_id = 4 兰德令（）限制4; [SqlFiddle here]（http://sqlfiddle.com/#!9/28922/1）
修改
道歉，最初，我不明白你想要实现的目标。如果您想要任何4个随机auction_items的最高出价（如果没有出价则为0），这里有一种方法可以使用2个派生表：

确定4个随机项目

查找每个auction_items
的最高出价
LEFT JOIN两个派生表一起

SELECT items.auction_item_id, IFNULL(topBids.amount, 0) as topBid FROM (SELECT auction_item_id FROM auction_item ORDER BY RAND() LIMIT 4 ) items LEFT JOIN (SELECT b.auction_item_id, b.amount FROM bid b GROUP BY b.auction_item_id ORDER BY amount DESC) topBids ON items.auction_item_id = topBids.auction_item_id;

Updated Fiddle

简单的SQL内连接查询 - 无法正常工作

3 个答案: