SQL集合操作中的WHERE子句

Question

请考虑以下查询，其中两个集合需要被相同的Location过滤。是否有更高效的/高效的方法，因此Location筛选器仅在两个套件中应用一次，或者您是否被迫分别对每个套件应用相同的筛选器？

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：并不想重构组操作每SE-它只是一个虚拟的例子。我的问题只是关于如何在集合操作中处理常用的WHERE子句。

Answer 1

您可以用CTE做到这一点：

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 

如果热膨胀系数不到位，你可以做同样的事情用视图。

Answer 2

我会重新因素的查询简单：

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' 

试试这个查询，并确保它取得相同的结果。

Answer 4

我会做这种方式：

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来处理设置的操作，并在不同平台上提供更大的支持。

我认为有些事情值得一提，一个总结：

1. 将最有可能表达第一。
2. 先放最少复杂的表情。
3. 使用更多和更少的搜索。

反向点1 & 2如果您使用Oracle，则由于从右到左评估而不是从左到右。