mysql得到一個值的重複

Question

有沒有辦法在mysql中檢查一個特定的列，看看值是否多出現一次，如果是的話就得到該行。

可以說，我的表看起來像這樣：

id | first_name | last_name | age 
1  john   doe  20 
.. .......  .....  ... 
.. .......  .....  ... 

所以我想MySQL的去，並帶回一個列表，其中年齡18以及其中FIRST_NAME出現更多然後一次。

Answer 1

SELECT y.id, y.first_name, y.last_name, y.age 
    FROM (SELECT first_name 
       FROM YourTable 
       WHERE age = 18 
       GROUP BY first_name 
       HAVING COUNT(*) > 1) t 
     INNER JOIN YourTable y 
      ON t.first_name = y.first_name 
    WHERE y.age = 18; 

Answer 2

select id, first_name, last_name, age 
from YourTable where first_name in 
(
    select first_name 
    from YourTable 
    where age = 18 
    group by first_name 
    having count(first_name) > 1 
) 

Answer 3

您可以使用JOIN：

SELECT DISTINCT T1.first_name 
FROM yourtable T1 
JOIN yourtable T2 
ON T1.id < T2.id 
AND T1.first_name = T2.first_name 
AND T2.age = 18 
WHERE T1.age = 18