Sql server 按公共列分组的多个表的值总和

我在MS SQL Server 2014中有三个表。它们中的每一个都包含一对数值、一个描述和一个日期。为了简洁起见，让我们假设下表：

table "beverages"

day        beverage amount
---------- -------- ------
2018-12-01 water    2
2018-12-01 tea      1
2018-12-01 coffee   7
2018-12-02 water    4
2018-12-02 tea      2


table "meals"

day        meal   amount
---------- ------ ------
2018-12-01 burger 1
2018-12-01 bread  2
2018-12-02 steak  1


table "fruit"

day        fruit  amount
---------- ------ ------
2018-12-01 apple  4
2018-12-01 banana 1
2018-12-02 apple  2

然后我有另一张桌子，上面只有一张日期表

table "dates"

day
----------
2018-12-01
2018-12-02

我需要的是一个查询，它为

dates

表中的每一行返回一行，每一行都有日期、饮料总量、膳食总量和当天水果总量。我不在乎不同种类的饮料、饭菜和水果，只在乎总数。结果应该是：

expected result

day        beverages   meals       fruit
---------- ----------- ----------- -----------
2018-12-01 10          3           5
2018-12-02 6           1           2 

但我收到的却是

received result

day        beverages   meals       fruit
---------- ----------- ----------- -----------
2018-12-01 40          18          30
2018-12-02 6           2           4

我已经知道问题是什么，只是不知道如何解决。更糟糕的是，我确信我曾经知道答案，但现在我甚至无法找到正确的搜索词让谷歌告诉我

当我这样做查询时（我使用表变量进行测试）

它对不同表中的每一行求和不止一次，因为它返回三个表的所有可能组合。删除SUM（）和GROUP BY证明：

day        beverages   meals       fruit
---------- ----------- ----------- -----------
2018-12-01 2           1           4
2018-12-01 2           1           1
2018-12-01 2           2           4
2018-12-01 2           2           1
2018-12-01 1           1           4
2018-12-01 1           1           1
2018-12-01 1           2           4
2018-12-01 1           2           1
2018-12-01 7           1           4
2018-12-01 7           1           1
2018-12-01 7           2           4
2018-12-01 7           2           1
2018-12-02 4           1           2
2018-12-02 2           1           2

---

那么，我需要在查询中做什么更改，使其对三个表中的每一个表的值求和，而不与其他表中的行数相乘呢？

换成PIVOT怎么样

示例

Select *
 From (
        Select day,Item='beverage',amount from beverages
        Union All
        Select day,Item='meals'   ,amount from meals
        Union All
        Select day,Item='fruit'   ,amount from fruit
      ) src
Pivot ( sum(amount) for Item in ([beverages],[meals],[fruit]) ) pvt

---

在连接前将表分组，如下所示：

SELECT 
     [d].[day]
    ,[b].[amount] AS [beverages]
    ,[m].[amount] AS [meals]
    ,[f].[amount] AS [fruit]
FROM @dates AS [d]
LEFT OUTER JOIN (SELECT day, SUM(amount) as amount FROM @beverages GROUP BY day) AS [b]
    ON [d].[day] = [b].[day]
LEFT OUTER JOIN (SELECT day, SUM(amount) as amount FROM @meals GROUP BY day) AS [m]
    ON [d].[day] = [m].[day]
LEFT OUTER JOIN (SELECT day, SUM(amount) as amount FROM @fruit GROUP BY day) AS [f]
    ON [d].[day] = [f].[day]

---

谢谢现在我读了你的答案，我想知道我怎么可能忘记了那件事。你刚刚救了我一天！还没有使用PIVOT查询，所以我选择了Richard的“加入前分组”解决方案，但这肯定是我应该习惯的，因为它看起来更灵活。谢谢你的回答@Patricketerbruch我相信有一天你会发现PIVOT会派上用场：）

SELECT 
     [d].[day]
    ,[b].[amount] AS [beverages]
    ,[m].[amount] AS [meals]
    ,[f].[amount] AS [fruit]
FROM @dates AS [d]
LEFT OUTER JOIN (SELECT day, SUM(amount) as amount FROM @beverages GROUP BY day) AS [b]
    ON [d].[day] = [b].[day]
LEFT OUTER JOIN (SELECT day, SUM(amount) as amount FROM @meals GROUP BY day) AS [m]
    ON [d].[day] = [m].[day]
LEFT OUTER JOIN (SELECT day, SUM(amount) as amount FROM @fruit GROUP BY day) AS [f]
    ON [d].[day] = [f].[day]