如何從SQL中提取唯一值？

Question

例如，假設我有下表

user_id, score
1,5
1,4
2,9
3,7
3,6
3,15
4,8
4,11

我想要一個返回user_id 2的查詢，因為它是唯一不重復的user_id

Answer 1

SELECT user_id FROM table GROUP BY(user_id) HAVING COUNT(user_id) = 1

Answer 2

select user_id 
from tableName
group by user_id 
having count(*)  = 1;

Answer 3

SELECT user_id 
FROM table
GROUP BY user_id
HAVING (COUNT(user_id)=1)