思路:
通過看評論大神和解題有以下幾種方法解決:
- 通過多表聯查;兩次訪問Person表,找到id不同但是Email相同的Email並輸出,需要注意的是要把輸出結果進行去重(distinct)。
- 通過分組;將Person表按照Email分組,並count出每個組中的Email總數,將大於1的Email輸出。【最快】
代碼:
select distinct p1.Email
from Person as p1,Person as p2
where p1.Email = p2.Email and p1.id != p2.id;
select Email
from Person
group by Email
having count(Email) >1