INTERSECT和WHERE IN有什么区别？

Question

我已经写了并且通过了70-433（SQL 2008 MCTS考试），并且当我意识到我一直在做什么INTERSECT与WHERE IN子查询以及EXCEPT与WHERE NOT IN子查询。

使用新命令而不是子查询有什么区别吗？

Answer 1

INTERSECT和EXCEPT比较返回的行中的所有选定值，而WHERE IN和WHERE NOT IN一次只比较一列。

SELECT name,date from customers 
EXCEPT 
SELECT name, date from orders 

Answer 2

有它们处理NULL小号

WITH T1 AS(SELECT 1 AS COL UNION SELECT NULL), 
    T2 AS (SELECT 2 AS COL UNION SELECT NULL) 
SELECT * FROM T1 
INTERSECT 
SELECT * FROM T2; 

一个重要的区别。

COL 
----------- 
NULL 

(1 row(s) affected) 

。

WITH T1 AS(SELECT 1 AS COL UNION SELECT NULL), 
    T2 AS (SELECT 2 AS COL UNION SELECT NULL) 
SELECT * FROM T1 WHERE COL IN (SELECT COL FROM T2) ; 

。

COL 
----------- 

(0 row(s) affected) 

。

WITH T1 AS(SELECT 1 AS COL UNION SELECT NULL), 
    T2 AS (SELECT 2 AS COL UNION SELECT NULL) 
SELECT * FROM T1 
EXCEPT 
SELECT * FROM T2; 

。

COL 
----------- 
1 

(1 row(s) affected) 

。

WITH T1 AS(SELECT 1 AS COL UNION SELECT NULL), 
    T2 AS (SELECT 2 AS COL UNION SELECT NULL) 
SELECT * FROM T1 WHERE COL NOT IN (SELECT COL FROM T2); 

。

COL 
----------- 

(0 row(s) affected)