Question

我有以下表格：

items(itemid, itemName, catid)

categories (catid, catname)

prices (itemid, open_price, close_price)

每个项目仅属于1个类别
每个项目在价格表中只有1个open_price，close_price行

如果我有10个类别，每个类别包含10个项目（例如），我如何找到每个类别中价格变化最大的公司。

我目前有一个运行的php循环并获得每个类别的最佳表现，但是想知道是否有办法更有效地完成它。

由于

代码：

foreach category, run the following query:

SELECT c.itemid, c.itemname ,

100.0 * ( cp.close_price - cp.open_price )/ IFNULL(cp.open_price,1) AS overall_change

FROM prices cp

LEFT JOIN items c ON c.itemid = prices.itemid

WHERE c.catid=8 ORDER BY overall_change DESC LIMIT 1;

Answer 1

如果你没有精神抽奖（当两个项目是一个类别的顶部时）

SELECT 
    cat.catid,
    cat.catname,
    c.itemid, 
    c.itemname ,
    100.0 * ( cp.close_price - cp.open_price )/ IFNULL(cp.open_price,1) AS overall_change    
FROM 
    categories AS cat
JOIN    
    items AS c
    ON cat.catid = c.catid
JOIN 
    prices AS cp
    ON c.itemid = cp.itemid
JOIN
    (SELECT
        c.catid, 
        MAX(100.0 * ( cp.close_price - cp.open_price )/ IFNULL(cp.open_price,1)) AS overall_change
    FROM   
        items AS c
    JOIN 
        prices AS cp
        ON c.itemid = cp.itemid
    GROUP BY
        c.catid
    ) AS max
    ON cat.catid = c.catid
    AND max.overall_change = (100.0 * ( cp.close_price - cp.open_price )/ IFNULL(cp.open_price,1))
ORDER BY
    cat.catid

......我还没有测试过这个：）

查询帮助（Foreach循环）

1 个答案: