In the SQL database query language, window functions allow access to data in the records right before and after the current record.[1][2][3][4] A window function defines a frame or window of rows with a given length around the current row, and performs a calculation across the set of data in the window.[5][6]
NAME | ------------ Aaron| <-- Preceding (unbounded) Andrew| Amelia| James| Jill| Johnny| <-- 1st preceding row Michael| <-- Current row Nick| <-- 1st following row Ophelia| Zach| <-- Following (unbounded)
In the above table, the next query extracts for each row the values of a window with one preceding and one following row:
SELECT LAG(name, 1) OVER(ORDER BY name) "prev", name, LEAD(name, 1) OVER(ORDER BY name) "next" FROM people ORDER BY name
The result query contains the following values:
| PREV | NAME | NEXT | |----------|----------|----------| | (null)| Aaron| Andrew| | Aaron| Andrew| Amelia| | Andrew| Amelia| James| | Amelia| James| Jill| | James| Jill| Johnny| | Jill| Johnny| Michael| | Johnny| Michael| Nick| | Michael| Nick| Ophelia| | Nick| Ophelia| Zach| | Ophelia| Zach| (null)|