SQL查詢不存在的

Question

這是我處理與該表的簡化版本是訂單

+-------------------+------------------+---------------+ 
| Order_Base_Number | Order_Lot_Number | Other Cols... | 
+-------------------+------------------+---------------+ 
|     1 |    3 |    | 
|     1 |    3 |    | 
|     1 |    4 |    | 
|     1 |    4 |    | 
|     1 |    4 |    | 
|     1 |    5 |    | 
|     2 |    3 |    | 
|     2 |    5 |    | 
|     2 |    9 |    | 
|     2 |    10 |    | 
+-------------------+------------------+---------------+ 

我想要做的是讓該計數基於基本和批號的唯一條目。我有兩組數字，一組是一組基數，另一組是一組批號。例如 ，可以說這兩套是Base In（1,2,3），Lot在（3,4,20）中。

我正在尋找一個SQL查詢，可以從兩組與展示多少次組合在表中找到的計數返回（基地地塊）的所有可能的組合。我的問題是我想包括所有可能的組合，如果一個組合不在訂單表中，我希望計數顯示爲零。所以，我正在尋找的輸出是這樣的。

+------+-----+-----------+ 
| Base | Lot | Frequency | 
+------+-----+-----------+ 
| 1 | 3 | 2  | 
| 1 | 4 | 3  | 
| 1 | 20 | 0  | 
| 2 | 3 | 1  | 
| 2 | 4 | 0  | 
| 2 | 20 | 0  | 
| 3 | 3 | 0  | 
| 3 | 4 | 0  | 
| 3 | 20 | 0  | 
+------+-----+-----------+ 

我試了很多查詢，但從來沒有接近這個，甚至不知道它是否可以完成。現在我正在搞清楚客戶端的組合，因此我正在執行太多的查詢來獲取頻率。

Answer 1

也許最清晰的方式是先從名單爲熱膨脹係數：

with bases as (
    select 1 as base from dual union all 
    select 2 as base from dual union all 
    select 3 as base from dual 
    ), 
    lots as (
    select 3 as lot from dual union all 
    select 4 as lot from dual union all 
    select 20 as lot from dual 
    ) 
select b.base, l.lot, count(Order_Base_Number) as Frequency 
from bases b cross join lots l left outer join 
    Orders o 
    on o.base = b.base and o.lot = l.lot 
group by b.base, l.lot 

注意，這使得cross join明確，特意不使用,的笛卡爾乘積。

此查詢的第一部分也可以寫成類似如下（假設每個基地，很多在表中的至少一個記錄）：

with bases as (
    select distinct base 
    from Orders -- or some other table, perhaps Orders ? 
    where base in (1, 2, 3) 
    ), 
    select distinct lot 
    from Orders -- or some other table, perhaps Lots ? 
    where lot in (3, 4, 20) 
    ) 
. . . 

這是更簡潔，但可能導致查詢效率較低。

Answer 2

你在最裏面的子查詢被稱爲CROSS JOIN，它得到的記錄笛卡爾產品（所有可能的組合）所需要的。這時候，你既沒有JOIN..ON condition也不WHERE你會得到什麼：

SELECT Base.Id as baseid, Lot.Id as lotid FROM Bases, Lots 

現在把它變成子查詢和LEFT JOIN到你的東西休息：

SELECT ... FROM 
    (SELECT Base.Id as baseid, Lot.Id as lotid 
      FROM Bases, Lots) baseslots 
    LEFT JOIN Orders ON Order_Base_Number = baseid, 
      Order_Lot_Number = lotid .... 

有了這個LEFT JOIN，你會得到爲NULL不存在的組合。使用COALESCE（或像這樣），把它們變成0

Answer 3

我沒有甲骨文測試，但這個是我會做什麼：

CREATE TABLE pairs AS 
(
SELECT DISTINCT Base.Order_Base_Number, Lot.Order_Lot_Number 
FROM ORDERS Base 
CROSS JOIN ORDERS Lot 
); 

CREATE TABLE counts AS 
(
SELECT Order_Base_Number, Order_Lot_Number, Count(*) AS C 
FROM ORDERS 
GROUP BY Order_Base_Number, Order_Lot_Number 
); 

SELECT P.Order_Base_Number, P.Order_Lot_Number, COALESCE(C.C,0) AS [Count] 
FROM Pairs P 
LEFT JOIN counts C ON P.Order_Base_Number = C.Order_Base_Number 
      AND P.Order_Lot_Number = C.Order_Lot_Number