Published on

June 13, 2010

Why You Should Avoid Cursors in SQL Server

SQL Server is a powerful relational database management system that allows developers and DBAs to perform a wide range of tasks using set-based SQL. However, there was a time when certain tasks couldn’t be accomplished with set-based SQL alone, and that’s when cursors came into play.

Cursors are a combination of SQL and procedural programming language that allow for more complex operations. They were introduced in the early 80s and initially seemed like the perfect solution to handle tasks that set-based SQL couldn’t handle on its own.

However, over time, it became clear that cursors had their drawbacks. They were slow, resource-intensive, and often resulted in code that was harder to read, understand, and maintain. Despite these issues, many developers continued to use cursors, either out of habit or because they were unaware of the alternatives.

With the release of SQL Server 2005, new features and capabilities were introduced that made cursors unnecessary in most cases. These features include large strings (VARCHAR(MAX), etc.), windowed aggregate functions (especially ROW_NUMBER()), and FOR XML PATH.

In this series of articles, we will explore why you should avoid cursors in SQL Server and how to achieve the same results using set-based SQL. We will demonstrate how these new and old features of Transact-SQL can help you create faster, smaller, cleaner, clearer, and more supportable SQL routines without the need for cursors or while loops.

So, why should you avoid cursors in SQL Server?

  1. Performance: Cursors are slow and resource-intensive. They often create temporary tables in tempdb and process rows one at a time, resulting in performance issues. Using cursors can also slow down other processes and cause blocking.
  2. Readability and maintainability: SQL routines with cursors are harder to read, understand, and maintain. Procedural code in SQL goes against the declarative nature of the language, making it more difficult to grasp the intent of the code.
  3. Availability: Cursors can tie up resources for a longer time, making them unavailable to other processes. This can lead to delays and bottlenecks in the system.
  4. Procedural thinking: Many developers are more familiar with procedural thinking and programming, which leads them to default to cursors as a solution. Declarative programming, on the other hand, requires a different mindset and approach.
  5. Lack of proficiency: SQL is often seen as a secondary skill for many developers, and they may not be fully proficient in it. This can lead to a reliance on cursors as a familiar solution, even when there are better alternatives.

In conclusion, cursors should be avoided in SQL Server whenever possible. The new features and capabilities introduced in SQL Server 2005 provide more efficient and effective ways to achieve the same results. By embracing set-based SQL and avoiding cursors, you can improve performance, readability, and maintainability of your code.

In the next article, we will dive deeper into the process of converting cursor-based code to set-based SQL. Stay tuned!

Author: R. Barry Young

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