SQL總和只有獨特價值

Question

我有一個包含以下內容的表：

plantId (pk) 
unitId 
maxCapacity 
numberOfPlants 
geographicalArea 
agreementStart 
agreementEnd 
plantType 

表包含以下數據：

1, A1, 10, 1, 3, 2013-01-01, 2013-12-31 
2, A2, 10, 1, 3, 2013-01-01, 2013-12-31 
3, A1, 10, 1, 3, 2013-03-01, 2013-12-31 

我想查詢我的表是這樣的：

SELECT DISTINCT 
    plantType, 
    geographicalArea, 
    sum(maxCapacity) as maxCapacity, 
    sum(numberOfPlants) as numberOfPlants, 
    count(unitId) as idCount 
FROM 
    tbl_plant 
WHERE 
    (agreementStart <= '2013-11-28' AND 
    agreementEnd >= '2013-11-28') AND 
    plantType <> '0' AND 
    plantType = '2' AND 
    geographicalArea = '3' 
GROUP BY 
    plantType, geographicalArea 

只要在r中每行返回一個唯一的unitId，此查詢就可以正常工作esultset。但是，如果第二次返回相同的unitId（請參見上面的A1），我不希望sum(maxCapacity)和sum(numberOfPlants)第二次包括該和，因爲它已經包含了它。

任何想法，我需要改變這個查詢？

Answer 1

使用內部查詢擺脫重複

SELECT plantType, geographicalArea, sum(maxCapacity) as maxCapacity, sum(numberOfPlants) as numberOfPlants, count(unitId) as idCount 
    FROM tbl_plant 
WHERE plantId in ( 
    SELECT MAX(plantId) 
    FROM tbl_plant 
    WHERE (agreementStart <= '2013-11-28' AND agreementEnd >= '2013-11-28') 
     AND plantType <> '0' 
     AND plantType = '2' 
     AND geographicalArea = '3' 
    GROUP BY unitId 
) 
GROUP BY plantType, geographicalArea