SQL集合操作中的WHERE子句

Question

請考慮以下查詢，其中兩個集合需要被相同的Location過濾。是否有更高效的/高效的方法，因此Location篩選器僅在兩個套件中應用一次，或者您是否被迫分別對每個套件應用相同的篩選器？

SELECT * 
FROM Orders 
WHERE Quantity BETWEEN 1 AND 100 
AND Location = 'SE' 

EXCEPT 

SELECT * 
FROM Orders 
WHERE Quantity BETWEEN 50 AND 75 
AND Location = 'SE'; 

注：並不想重構組操作每SE-它只是一個虛擬的例子。我的問題只是關於如何在集合操作中處理常用的WHERE子句。

Answer 1

您可以用CTE做到這一點：

with ord (Column1, Column2) as 
(
    SELECT Column1, Column2 
    FROM Orders 
    WHERE Location = 'SE' 
) 
SELECT * 
FROM ord 
WHERE Quantity BETWEEN 1 AND 100 

EXCEPT 

SELECT * 
FROM ord 
WHERE Quantity BETWEEN 50 AND 75 

如果熱膨脹係數不到位，你可以做同樣的事情用視圖。

Answer 2

我會重新因素的查詢簡單：

SELECT * 
FROM Orders 
WHERE Quantity BETWEEN 1 AND 100 
AND Quantity NOT BETWEEN 50 AND 75 
AND Location = 'SE'; 

Answer 3

SELECT * 
FROM Orders 
WHERE ((Quantity BETWEEN 1 AND 49) OR (Quantity BETWEEN 76 AND 100)) 
AND Location = 'SE' 

試試這個查詢，並確保它取得相同的結果。

Answer 4

我會做這種方式：

SELECT * 
FROM Orders 
WHERE ((Quantity BETWEEN 1 AND 49) 
OR (Quantity BETWEEN 76 AND 100)) 
AND Location = 'SE'; 

Answer 5

SELECT * 
FROM Orders o1 
WHERE Quantity BETWEEN 1 AND 100 
AND Location = 'SE' 
AND NOT EXISTS (SELECT 1 FROM ORDERS o2 
       WHERE QUANTITY BETWEEN 50 AND 75 
       AND Location = 'SE' 
       AND o1.ORDERS_ID = o2.ORDERS_ID) 

Answer 6

您可以使用AND NOT而不是EXCEPT來處理設置的操作，並在不同平臺上提供更大的支持。

我認爲有些事情值得一提，一個總結：

1. 將最有可能表達第一。
2. 先放最少複雜的表情。
3. 使用更多和更少的搜索。

反向點1 & 2如果您使用Oracle，則由於從右到左評估而不是從左到右。