SQL查詢 - 某種選擇不同？

Question

假設我有一個日誌誰在特定天數，如客戶有：

Cs day 
-- --- 
01 Tue 
02 Tue 
03 Wed 
01 Wed 
04 Thu 
02 Thu 

我需要返回只有那些誰在無論在星期二和星期三客戶的＃分別查詢在這種情況下，只有CS＃01

Answer 1

select distinct c1.Cs 
from Customers c1 
inner join Customers c2 on c2.Cs=c1.Cs 
where c2.day='Tue' and c1.day='Wed' 

Answer 2

而且使用子查詢...

Select distinct cs From Customers 
Where Exists (Select * from Customers 
       Where day = 'Tue') 
    And Exists (Select * from Customers 
       Where day = 'Wed')