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Cursors

A CURSOR is a database object used to retrieve, manipulate, and navigate through a result set row by row. Cursors are useful for processing individual rows returned by a query, especially when performing complex operations that require row-by-row analysis.

Declaring and Using a Cursor

The steps to use a cursor are:

  1. Declare the cursor with the desired query.
  2. Open the cursor to establish the result set.
  3. Fetch rows from the cursor into variables.
  4. Close the cursor when done.
  5. Deallocate the cursor to free resources.

Example: Using a Cursor

DECLARE @Name VARCHAR(50), @City VARCHAR(50);

DECLARE fighter_cursor CURSOR FOR
SELECT Name, City FROM FreedomFighters;

OPEN fighter_cursor;
FETCH NEXT FROM fighter_cursor INTO @Name, @City;

WHILE @@FETCH_STATUS = 0
BEGIN
    PRINT 'Freedom Fighter: ' + @Name + ', City: ' + @City;
    FETCH NEXT FROM fighter_cursor INTO @Name, @City;
END;

CLOSE fighter_cursor;
DEALLOCATE fighter_cursor;

Output:

Prints each freedom fighter's name and city row by row.

When to Use Cursors

Cursors should be used when row-by-row processing is necessary, such as:

  • Complex operations that cannot be performed with a set-based approach.
  • Data migration or transformation tasks.

Do's and Don'ts

Do's

  • Use cursors when set-based operations are not feasible.
  • Always close and deallocate cursors to free up resources.
  • Use cursors efficiently and minimize their use in high-traffic environments.

Don'ts

  • Don't use cursors for operations that can be performed using set-based queries; they are more efficient.
  • Don't leave cursors open, as it can lead to performance issues.
  • Don't use cursors unnecessarily in large datasets; consider alternative approaches first.
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