Question

考虑以下查询，其中两个集合都需要通过相同的Location进行过滤。是否有更高效/高效的方法，Location过滤器只在两个集合中应用一次，或者您是否被迫对每个集合应用相同的过滤器？

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';

注意：不打算重构设置操作本身只是一个虚拟的例子。我的问题只是关于如何处理集合操作中的常见WHERE子句。

Answer 1

我会将查询重新计算为：

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

Answer 2

您可以使用CTE：

执行此操作

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CTE不可用，您可以使用视图执行相同的操作。

Answer 3

您可以使用AND NOT而不是EXCEPT [1]来处理设置操作，并在不同平台上提供更多支持。

我认为值得一提的是一个总结：

首先放置最不可能的表达。
首先放置最不复杂的表达式。
使用更多和更少的搜索。

反向点1＆amp;如果您使用Oracle，则由于从右到左的评估，而不是从左到右。

Answer 4

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

尝试此查询并确保其获取相同的结果。

Answer 5

我会这样做：

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

Answer 6

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)

跨SQL集操作的WHERE子句

6 个答案: