Question

我想为每个位置选择最受欢迎的菜单项。有什么建议？？

SELECT a.City, a.ItemName, a.Quantity
    FROM
            (SELECT TOP 1
                    l.city AS City,
                    mi.name AS ItemName,
                    SUM(ft.quantity_sold) AS Quantity
            FROM
                    FactTable ft
                            JOIN MenuItem mi ON (ft.menuItemID = mi.ID)
                            JOIN Location l ON (ft.locationID = l.ID)
            ORDER BY
                    Quantity DESC
            GROUP BY
                    l.city, mi.name;
            ) AS a

Answer 1

也许这......获得每个城市和菜单项名称的最大金额。返回顶部返回1行而不是每组一行。你需要使用max aggregate来按照你想要的方式工作。

你不能加倍聚合最大值（总和（数量）），所以你必须使用子选择，或使用CTE（公用表表达式）。这是子选择。

Select city, itemName, max(Quantity)
FROM (
            SELECT 
                    l.city AS City,
                    mi.name AS ItemName,
                    SUM(ft.quantity_sold) AS Quantity
            FROM
                    FactTable ft
                            JOIN MenuItem mi ON (ft.menuItemID = mi.ID)
                            JOIN Location l ON (ft.locationID = l.ID)
            GROUP BY
                    l.city, mi.name) sub
GROUP BY City, ItemName;

从每个组sql中选择前1位

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