Introduction
When it comes to SQL Server, there are certain concepts and practices that can greatly impact performance. One such concept is the use of cursors and loops. While they may seem necessary at times, they can often be a source of performance issues. In this article, we will explore an example where the use of cursors and loops was causing performance problems, and how they were replaced with more efficient alternatives.
The Problem
In a recent project, we encountered a piece of code that was performing poorly. The code used inner cursors embedded in an outer cursor to pivot data from a one-to-many table into a single column of an output table. This approach involved a lot of overhead, such as declaring, opening, fetching, closing, and deallocating cursors. As a result, the code was running very slowly.
The Solution
To improve the performance of the code, we decided to replace the cursors and loops with more efficient alternatives. First, we replaced the inner cursors with a direct column pivot into a variable. This eliminated the need for the inner cursor and significantly improved the performance of that part of the code.
Next, we looked at the outer cursor and realized that the select statement within it could be optimized further. We decided to create a scalar function that would perform the same operation as the select statement. This allowed us to eliminate the outer cursor and replace it with a single update statement that called the function.
The Results
The improvements we made to the code had a significant impact on performance. The section of the code that previously took 52 minutes to execute now took only about 11 minutes. Furthermore, after replacing the outer cursor with the scalar function, the entire job dropped from 1 hour 20 minutes to just over 12 minutes.
Conclusion
Based on our experience, we highly recommend replacing manual looping code with function calls in SQL Server, especially when dealing with large data sets. By eliminating the use of cursors and loops, you can greatly improve the performance of your code and achieve faster execution times.
Remember, when it comes to SQL Server, optimizing performance is crucial. By understanding the impact of certain concepts, such as cursors and loops, and finding more efficient alternatives, you can ensure that your code runs smoothly and efficiently.