INTERSECT和WHERE IN有什麼區別？

Question

我已經寫了並且通過了70-433（SQL 2008 MCTS考試），並且當我意識到我一直在做什麼INTERSECT與WHERE IN子查詢以及EXCEPT與WHERE NOT IN子查詢。

使用新命令而不是子查詢有什麼區別嗎？

Answer 1

INTERSECT和EXCEPT比較返回的行中的所有選定值，而WHERE IN和WHERE NOT IN一次只比較一列。

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

Answer 2

有它們處理NULL小號

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; 

一個重要的區別。

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)