Question

我有很多团体。每个组条目由另一个组条目拥有。例如，soccer club组拥有soccer training，soccer cardio squad，pro training和beginner training。我想找出哪个组拥有最多的training 类型组。为了确定哪个组属于彼此，我有一个名为groupOwnedBy()的函数，该函数返回拥有该组的id组。

例如，如果我们要检查哪个组拥有soccer training，我们传入2，因为这是soccer training的ID

SELECT * FROM groupOwnedBy(2);

将返回拥有1的组soccer training的ID（表示它是soccer club所拥有的）

groupOwnedBy
------------
1

SELECT * from groupOwnedBy(1); -- will return 1. soccer club is owned by soccer club

我要打印拥有最多训练类型组的组的名称。在这种情况下，它应该打印soccer club。

CREATE TABLE groups (
  id integer primary key,
  type text NOT NULL,
  name text
);


INSERT INTO groups (id, type, name) VALUES
(1, 'owner', 'soccer club'),          -- owned by soccer club
(2, 'training', 'soccer training'),   -- owned by soccer club
(3, 'cardio', 'soccer cardio squad'), -- owned by soccer club
(4, 'training', 'pro training'),      -- owned by soccer club
(5, 'training', 'beginner training'), -- owned by soccer club
(6, 'cardio', 'Cricket cardio team'), -- owned by cricket club
(7, 'owner', 'Cricket club'),         -- owned by cricket club
(8, 'training', 'Cricket training'),  -- owned by cricket club
(9, 'owner', 'Hockey club'),          -- owned by Hockey club
(10, 'owner', 'Kids Hockey')          -- owned by Hockey club
(11, 'training', 'smart train'),      -- owned by Hockey club
(12, 'training', 'fit train');        -- owned by Hockey club

我尝试过

SELECT name
FROM group
WHERE type = 'training'
GROUP BY ownedByGroup(id)
ORDER BY COUNT(*) DESC
LIMIT 1;

但我不断收到错误消息：

ERROR: column "name" must appear in the GROUP BY clause or be used in an aggregate function

Answer 1

您将按ownerByGroup（id）表达式分组并获得最大计数（*）。

之后，您将与组表联接，以便按照以下方式查找与id对应的名称

select y.name,y.id 
  from (
    SELECT ownedByGroup(id) as max_training_grp_id
          ,count(*)
      FROM group
     WHERE type = 'training'
    GROUP BY ownedByGroup(id)
    ORDER BY COUNT(*) DESC
    LIMIT 1
       )x
   join group y
     on x.max_training_grp_id=y.id

找出哪个小组的培训人数最多

1 个答案: