SQL检查一个列表与另一个

Question

我很感激任何关于如何在SQL中检查一个列表中的元素是否也出现在另一个列表中的指针。

List A = Live Customers in April 
List B = Live Customers in May 

如何检查列表B中的哪些客户也出现在列表B中？以识别那些已经丢失的客户

i.e. Customers in A but not in B. 

谢谢你的帮助。 GAV

Answer 1

尝试not in条款

例如

select * 
from mytable 
where id not in (select id from table2) 

这会返回结果不在另一个表。快速和简单的

Answer 2

不同的方法来拉动的结果

SELECT customer 
FROM ListA a 
WHERE NOT EXISTS (SELECT 1 FROM ListB b WHERE a.customer=b.customer) 

OR

SELECT a.customer 
FROM ListA a 
    LEFT JOIN ListB b ON a.customer=b.customer 
WHERE b.customer is null 

OR

SELECT customer 
FROM ListA 

except 

SELECT customer 
FROM ListB 

OR

SELECT customer 
FROM ListA 
WHERE customer NOT IN (SELECT customer FROM ListB)