Syntax
------

NTH_VALUE (expr[, num_row]) OVER ( 
 [ PARTITION BY partition_expression ]
 [ ORDER BY order_list ]
)

Description
-----------

The NTH_VALUE function returns the value evaluated at row number num_row of
the window frame, starting from 1, or NULL if the row does not exist.

URL: https://mariadb.com/kb/en/nth_value/