16.20 - Example - Advanced SQL Engine - Teradata Database

The functions are going to return the first/last value in the window. In the example, the first and last rows fall within the window. If the window were between 3 preceding and 2 preceding rows, you would see NULL for first value in the 1st two rows.

SELECT start_date, salary,
       AVG(salary) OVER(ORDER BY start_date
       ROWS BETWEEN 3 PRECEDING AND 1 FOLLOWING) ma,
       FIRST_VALUE(salary) OVER(ORDER BY start_date
       ROWS BETWEEN 3 PRECEDING AND 1 FOLLOWING) first,
       LAST_VALUE(salary) OVER(ORDER BY start_date
       ROWS BETWEEN 3 PRECEDING AND 1 FOLLOWING) last
FROM employee
ORDER BY start_date;