🧵 SQL CURSORS – Complete Guide with Syntax & Examples

🧲 Introduction – Why Use SQL Cursors?

SQL is designed to handle set-based operations efficiently. However, there are times when you need to process records one row at a time—like generating custom reports, performing procedural logic, or iterating through complex datasets. That’s where SQL Cursors come in.

A cursor in SQL acts like a pointer that traverses a result set row-by-row. While not ideal for performance, they provide essential control in scenarios where row-level processing is unavoidable.

🎯 In this guide, you’ll learn:

• What cursors are and how they work
• Cursor types and lifecycle
• Syntax and examples across databases
• Best practices and performance tips

🔑 1. What Are SQL Cursors?

A cursor is a temporary work area created in the system memory where the result set is stored. It enables row-by-row processing rather than the typical set-based processing.

🔁 2. Cursor Workflow Steps

🛠️ 3. SQL Server Cursor Example

DECLARE @Name VARCHAR(50);

DECLARE employee_cursor CURSOR FOR
SELECT name FROM employees;

OPEN employee_cursor;

FETCH NEXT FROM employee_cursor INTO @Name;

WHILE @@FETCH_STATUS = 0
BEGIN
    PRINT 'Employee Name: ' + @Name;
    FETCH NEXT FROM employee_cursor INTO @Name;
END;

CLOSE employee_cursor;
DEALLOCATE employee_cursor;

✅ Explanation:

• DECLARE CURSOR – Sets up the result set.
• OPEN – Loads the rows.
• FETCH NEXT – Iterates through rows.
• @@FETCH_STATUS – Checks for end of result set.

🔎 4. MySQL Cursor Example (Stored Procedure)

DELIMITER //

CREATE PROCEDURE list_names()
BEGIN
  DECLARE done INT DEFAULT FALSE;
  DECLARE emp_name VARCHAR(100);
  DECLARE cur CURSOR FOR SELECT name FROM employees;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  OPEN cur;

  read_loop: LOOP
    FETCH cur INTO emp_name;
    IF done THEN
      LEAVE read_loop;
    END IF;
    SELECT emp_name;
  END LOOP;

  CLOSE cur;
END //

DELIMITER ;

✅ Explanation:

• MySQL cursors must be used inside stored procedures.
• HANDLER FOR NOT FOUND is used to exit the loop.

🧪 5. Cursor Types in SQL Server

💡 Use FORWARD_ONLY for best performance when possible.

📘 Cursor Use Cases

💡 Best Practices & ⚠️ Gotchas

📊 Cursor vs WHILE Loop

📌 Summary – Recap & Next Steps

SQL Cursors provide row-by-row control over data, useful in specific scenarios like report generation, data validation, or when looping is required. Use them wisely due to their performance cost.

🔍 Key Takeaways:

• SQL Cursors are ideal for procedural row-level operations.
• Must follow a clear DECLARE → OPEN → FETCH → CLOSE → DEALLOCATE pattern.
• Always evaluate if a set-based alternative is more efficient.

⚙️ Real-World Relevance:
Cursors are used in data migration scripts, legacy systems, and batch-processing jobs in banking, ERP, and data warehousing systems.

❓ FAQ – SQL Cursors

❓ When should I use a SQL Cursor?

✅ Use cursors when you need row-by-row logic like custom calculations, auditing, or sequential data transformation.

❓ Are SQL Cursors bad for performance?

✅ Yes, they are slower than set-based operations. Use them only when necessary and keep logic minimal.

❓ Can I update data using a cursor?

✅ Yes, but only with updatable cursors. Be cautious as this can lead to locks or performance issues.

❓ What’s the alternative to cursors?

✅ Use window functions, ROW_NUMBER(), CTEs, or WHILE loops with set operations when possible.

❓ Are cursors supported in all databases?

✅ Yes, but the syntax varies. Example:

• SQL Server: supports full cursor control.
• MySQL: only in stored procedures.
• PostgreSQL: supports cursors with DECLARE and FETCH.