In SQL Server, when you declare a cursor, you can specify options that determine how the cursor behaves. Two of these options are FORWARD_ONLY and SCROLL.
FORWARD_ONLY Cursor
A FORWARD_ONLY cursor allows you to iterate through a result set in a forward direction only. This means that once you move to the next row, you cannot go back to the previous rows. This type of cursor is generally faster and consumes less memory since it doesn't keep track of the entire result set in both directions.
SCROLL Cursor
A SCROLL cursor, on the other hand, allows you to move through the result set in any direction: forward, backward, and even be positioned on specific rows. This makes it more flexible, but it can be more resource-intensive than a FORWARD_ONLY cursor as it has to maintain more information about the result set.
Syntax for Cursor Declaration
When declaring a cursor, you can specify these options as part of the cursor declaration. Here's an example illustrating how both options can be used:
Example of FORWARD_ONLY Cursor
DECLARE cursor1 CURSOR FORWARD_ONLY FOR
SELECT column1, column2
FROM your_table;
OPEN cursor1;
FETCH NEXT FROM cursor1; -- Move to the first row
-- Process the row
FETCH NEXT FROM cursor1; -- Move to the next row
CLOSE cursor1;
DEALLOCATE cursor1;
Example of SCROLL Cursor
DECLARE cursor2 CURSOR SCROLL FOR
SELECT column1, column2
FROM your_table;
OPEN cursor2;
FETCH FIRST FROM cursor2; -- Move to the first row
FETCH LAST FROM cursor2; -- Move to the last row
FETCH PRIOR FROM cursor2; -- Move to the previous row
FETCH NEXT FROM cursor2; -- Move to the next row
CLOSE cursor2;
DEALLOCATE cursor2;
Key Points
1. FORWARD_ONLY:
- Can only access rows one at a time in a forward direction.
- More efficient in terms of performance.
- Ideal for scenarios where you only need to read through the data.
2. SCROLL:
- Can access rows in any direction (next, previous, first, last).
- More flexible but can consume more resources.
- Useful when you need complex navigation through the result set.
When deciding between the two, consider both the flexibility required and the performance implications based on the tasks that will be performed with the cursor.