使用SQL進行分組時計算行之間的差異

Question

我有一個postgresql表，其中包含倉庫間不同項目（模型）的移動。

例如，以下記錄意味着，5個單位的模型1的已發送形式倉庫1至2：

source target model units 
------ ------ ----- ----- 
    1  2  1  5 

我試圖建立一個SQL查詢來獲得發送和接收單元之間的差，按模型分組。再一個例子：

source target model units 
------ ------ ----- ----- 
    1  2  1  5 -- 5 sent from 1 to 2 
    1  2  2  1 
    2  1  1  2 -- 2 sent from 2 to 1 
    2  1  1  1 -- 1 more sent from 2 to 1 

結果應該是：

source target model diff 
------ ------ ----- ---- 
    1  2  1 2 -- 5 sent minus 3 received 
    1  2  2 1 

我不知道這是否可能與一個SQL查詢。

下面是表創建腳本和一些數據，以防萬一有人想嘗試一下：

CREATE TEMP TABLE movements 
(
    source INTEGER, 
    target INTEGER, 
    model INTEGER, 
    units INTEGER 
); 

insert into movements values (1,2,1,5); 
insert into movements values (1,2,2,1); 
insert into movements values (2,1,1,2); 
insert into movements values (2,1,1,1); 

Answer 1

這是做你所需要的嗎？我沒有一個Oracle數據庫再次進行測試，所以我希望在分組表達式規則是相同的MS SQL Server

SELECT  
CASE WHEN source < target THEN source ELSE target END AS source, 
CASE WHEN source < target THEN target ELSE source END AS target, 
SUM(CASE WHEN source < target THEN units ELSE -units END) AS Diff, 
    model 
FROM movements 
GROUP BY 
CASE WHEN source < target THEN source ELSE target END, 
CASE WHEN source < target THEN target ELSE source END, 
    model 

Answer 2

您可以用兩個子查詢該款項在各個方向的運動，然後工會和sum做到這一點這兩個子查詢的結果如下：

SELECT source, target, model, SUM(units) 
FROM (
    SELECT source, target, model, SUM(units) AS units 
    FROM movements 
    WHERE source < target 
    GROUP BY source, target, model 
    UNION ALL 
    SELECT target, source, model, SUM(-units) AS units 
    FROM movements 
    WHERE source > target 
    GROUP BY source, target, model 
) T1 
GROUP BY source, target, model