SQL检查一个列表对另一个

Question

我很感激有关如何在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示。

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

如何查看列表A中哪些客户也出现在列表B中？识别那些已经失去的客户

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

感谢您的帮助。 GAV

Answer 1

提取结果的不同方法

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 )

Answer 2

尝试not in子句

示例

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

这将返回不在另一个表中的结果。快速简单