Window function: returns the value that is the offsetth row of the window frame
(counting from 1), and null if the size of window frame is less than offset rows.
It will return the offsetth non-null value it sees when ignoreNulls is set to
true. If all values are null, then null is returned.
This is equivalent to the nth_value function in SQL.
New in version 3.1.0.
name of column or expression
number of row to use as the value
indicates the Nth value should skip null in the
determination of which row to use