Question

我正在开发的应用程序中使用SQLite 我正在尝试运行一个非常复杂的查询（对我而言很复杂！）并且我已经得到了我需要的基本结果但我仍然坚持克服最后一道障碍。

我现在有这个查询可以做我需要做的事情......

SELECT SUM(activity)
FROM activities
WHERE activity_id IN(SELECT name_id FROM foods GROUP BY name_id HAVING SUM(points) > 20);

我需要在此查询中添加另一部分，但这对我来说有点复杂。有三个表....日期，食物，活动，我需要找到一个结果集的总和，只要某个陈述为真，它就包含两个不同表中两个值之间的最小数字。

基本上......

SELECT SUM(total) FROM (SELECT MIN(value from table1 which is determined by a value in table2, value from table3) AS total
FROM table3
WHERE value from table3 is contained in a result set from table1);

以下查询是我提出的，如果没有任何语法（lol！），它将起作用。这不起作用，但我只想表明它，以便更好地了解我正在尝试做什么。

SELECT SUM(activity_amount) FROM (SELECT min((SELECT SUM(points) - 20 FROM foods WHERE name_id IN(SELECT pk FROM dates WHERE weekly=1) GROUP BY name_id), activity) AS activity_amount
FROM activities
WHERE activity_id IN(SELECT name_id FROM foods GROUP BY name_id HAVING SUM(points) > 20));

问题在于MIN() ....

中的第一个值

SELECT SUM(points) - 20 FROM food WHERE name_id IN(SELECT pk FROM dates WHERE weekly=1) GROUP BY name_id

该语句产生多个值，但即使我确实需要将这些值与MIN()中的其他值进行比较，我一次只需要一个...而不是整个集合。

我怎样才能获得上面创建的上述查询？

编辑...一些示例表可以提供更好的帮助。谢谢jellomonkey和hainstech

Table#1(dates)  

CREATE TABLE dates (pk INTEGER PRIMARY KEY, date INTEGER, weekly INTEGER)
pk  date       weekly
1   05062009    1  
2   05072009    1  
3   05082009    2 

Table #2(foods)  

CREATE TABLE foods (pk INTEGER PRIMARY KEY, food VARCHAR(64), points DOUBLE, name_id INTEGER)
pk   food   points   name_id  
 1   food1    12.0     1  
 2   food2    9.0      1  
 3   food3    5.0      1  
 4   food4    15.0     2
 5   food5    14.0     2  
 6   food6    12.0     3  

Table#3(activities)  

CREATE TABLE activities (pk INTEGER PRIMARY KEY, activity DOUBLE, activity_id INTEGER)
pk   activity   activity_id
 1     5.0           1  
 2     4.0           1  
 3     2.0           2  
 4     4.0           3

使用我的原始帖子（一个不起作用）的ex和查询，我会寻找一个包含一个值的结果集.8.0

MIN（26.0-20,9.0）= 6.0
MIN（29.0-20,2.0）= 2.0
6.0 + 2.0 = 8.0

我希望这有帮助！

Answer 1

经过多次头疼和占卜后，我怀疑你想要的是什么：

SELECT SUM(MIN(fp-20, ap)) FROM
  (SELECT dates.pk AS fd, SUM(points) AS fp
  FROM dates
  JOIN foods ON name_id = fd
  GROUP BY fd
  HAVING fp >= 20)
    JOIN
  (SELECT dates.pk AS ad, SUM(activity) AS ap
  FROM dates
  JOIN activities ON activity_id = ad
  GROUP BY ad)
    ON fd = ad

列名似乎与它们的含义没有任何联系，但是，嘿，至少这确实给出了8.0，而subselects给出了你提到的其他数字！ - ）

Answer 2

同意jellomonkey - 除非你显示更多信息，否则我无法理解你想要什么。简单的表定义，几行示例数据和预期的输出都会有所帮助。

这是一个简单的例子，用于根据在其他两个表中定义其边界的范围从表中获取最小值：

create table t1(t1id int primary key, value int)
create table t2(t1id int, t2id int primary key, value int)
create table t3(t2id int, t3id int primary key, value int)

select
    MIN(t1.value)
from table1 as t1 
    join table2 as t2 on t2.t1id = t1.t1id
    join table3 as t3 on t3.t2id = t2.t2id
where t1.value between t2.value and t3.value

这使用t2.value和t3.value作为范围的边界来查找MIN（）。

编辑 - 感谢发布样本表，这有助于增加收益。您可以使用一些复杂的CASE语句来比较这两个值，但我会将它们放入一个行集并进行正常的MIN聚合。这将更具可读性，并且如果需要，还可以让您更轻松地添加一组额外信息以包含在MIN输入中。所以这是对我要做的事情的快速打击：

select
    SUM(activity)
from (
    select
        min(activity) as activity
        ,activity_id
    from (
        select
            SUM(activity) as activity, activity_id
        from activities 
        group by activity_id
        union all
        select
            SUM(points)-20
            ,name_id
        from foods 
        group by name_id
        having SUM(points) > 20
    ) as activitySum
    where activity_id in (select pk from dates where weekly=1)
    group by activity_id
) as activityLesserOf

编辑＃2 - 根据需要澄清添加到上述查询

使用Min（）SQL使用多个表，多个值

2 个答案: