查找SQL中第N大元素

Question

想知道如何編寫SQL函數來查找表中第N個最大元素，如果沒有第N個最大元素，則返回Null。

使用MySQL/MySQL工作臺。

順便說一句，我的問題與第N個最高工資問題不同，因爲我有一個附加要求，如果第N個最大元素不存在，則返回Null。任何想法都表示讚賞。

在此先感謝， 林

Answer 1

你可以這樣做：

SELECT t1.* 
FROM (
    SELECT * 
    FROM my_table 
    ORDER BY value DESC 
    LIMIT 1 
    OFFSET N -- Set your value for N here, N being 0-based 
) t1 
RIGHT OUTER JOIN (
    SELECT null -- This will guarantee that you have at least one row 
) t2 
ON TRUE 

Answer 2

我能想到的任何情況下，我會想這樣做的......

SELECT * FROM ints; 
+---+ 
| i | 
+---+ 
| 0 | 
| 1 | 
| 2 | 
| 3 | 
| 4 | 
| 5 | 
| 6 | 
| 7 | 
| 8 | 
| 9 | 
+---+ 

SELECT CASE WHEN COUNT(*) = 9 THEN x.i ELSE NULL END i 
    FROM ints x 
    JOIN ints y 
    ON y.i <= x.i 
GROUP 
    BY x.i 
ORDER 
    BY i DESC 
LIMIT 1; 
+------+ 
| i | 
+------+ 
| 8 | 
+------+ 

SELECT CASE WHEN COUNT(*) = 11 THEN x.i ELSE NULL END i 
    FROM ints x 
    JOIN ints y 
    ON y.i <= x.i 
GROUP 
    BY x.i 
ORDER 
    BY i DESC 
LIMIT 1; 
+------+ 
| i | 
+------+ 
| NULL | 
+------+ 

Answer 3

SELECT *from Employee_Test_salary 
 

 
go 
 

 
with emplsal as(
 
\t SELECT Emp_Sal ,DENSE_RANK() over (order by Emp_Sal desc) as rownumber 
 
\t from Employee_Test_salary 
 
) 
 
select top 1 Emp_Sal from emplsal where emplsal.rownumber =N