SA0107 : Avoid using procedural logic with a cursor

Using cursors, while sometimes necessary, often leads to performance issues because they process one row at a time rather than set-based operations. This can be inefficient and slow, especially on large datasets.

For example:

1-- Example of problematic cursor usage
2DECLARE myCursor CURSOR FOR
3SELECT ColumnName FROM TableName;
4OPEN myCursor;
5FETCH NEXT FROM myCursor INTO @Variable;
6-- Additional cursor processing...
7CLOSE myCursor;
8DEALLOCATE myCursor;

This approach is problematic as it iterates through the result set row by row, potentially leading to high CPU usage and longer execution times compared to set-based operations.

• Decreased performance due to row-by-row processing instead of leveraging SQL Server’s set-based processing capabilities.

• Increased complexity and potential for errors in the code because cursors require explicit open, fetch, close, and deallocate operations.

Improve performance by replacing cursors with set-based operations when possible.

Follow these steps to address the issue:

1. Analyze the current cursor-based implementation to understand its purpose and the data transformation it performs. Examine the existing DECLARE, OPEN, FETCH, CLOSE, and DEALLOCATE statements to identify the target table and columns involved.

2. Conceptualize how the same data transformation can be achieved through a set-based approach. This often involves using SELECT, JOIN, WHERE, and other set-based SQL operations to achieve similar logic in a single query.

3. Refactor the cursor code into a set-based SQL query. This may include combining related tables using JOIN, filtering using WHERE clauses, and applying operations directly within the query.

4. Test the refactored query to ensure it produces the same results as the cursor-based implementation but with improved performance. Verify the logic and correctness of the output against expected results.

For example:

1-- Example of set-based query replacing a cursor
2SELECT ColumnName
3FROM TableName
4-- Additional set-based operations if necessary...

The rule has a Batch scope and is applied only on the SQL script.

Rule has no parameters.

The rule does not need Analysis Context or SQL Connection.

Design Rules, Bugs

DECLARE CURSOR (Transact-SQL)

Other Resources