创建总和的视图，选择min并选择子表的最大值

Question

我有3个表，我想加入一个视图

委员会表：

idCommission: int
name:         varchar
...

季节：

idSeason:     int
since:        date
till:         date

Seasons_in_commission：

idCommission: int
idSeason:     int

结果视图：

idCommission: int    | ID for referencing
Commission.*         | All other from Commission table
since:        date   | Min of all its (from) seasons
till:         date   | Max of all its (till) seasons
seasons:      int    | Count of its seasons

我试过，但我发现，我需要在子查询中逐行引用，我不知道该怎么做。

SELECT Commission.*, 
MIN(
  SELECT since FROM Seasons_in_commission 
  JOIN Season USING(idSeason) 
  WHERE idCommission = currentRow.idCommission /*<- this part is wrong */
) as Since, MAX(...) as Till, COUNT(...) as Seasons FROM Commission

Answer 1

我认为你不需要任何子查询。试试这个：

SELECT Commission.*, MIN(since) AS Since, MAX(till) AS Till, COUNT(*) AS Seasons
  FROM Commission
  JOIN Seasons_in_commission USING (idCommission)
  JOIN Season USING (idSeason)
 GROUP BY idCommission;

（请注意，这只适用于ONLY_FULL_GROUP_BY已禁用。）