FIRST_VALUE uses the value of the field column from the first row to assign to all rows in the specific window frame. FIRST_VALUE supports the ROWS clause.
Note that the NULL collates before all values, so if the value of field in the first row is NULL, all of the rows in the window will be NULL.
A column that specifies which value to assign to all rows in that window frame.
The following example returns the first value of the Country column within each city:
SELECT FIRST_VALUE(Country) OVER (PARTITION BY City)