How to Optimize Your SQL Query for Efficient Execution скачать в хорошем качестве

How to Optimize Your SQL Query for Efficient Execution

Learn how to streamline your SQL query execution plan and reduce costs using efficient coding techniques. --- This video is based on the question https://stackoverflow.com/q/68099045/ asked by the user 'banana_99' ( https://stackoverflow.com/u/16119285/ ) and on the answer https://stackoverflow.com/a/68099127/ provided by the user 'Gordon Linoff' ( https://stackoverflow.com/u/1144035/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Execution plan too expensive case when exists Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- How to Optimize Your SQL Query for Efficient Execution When it comes to managing databases, achieving optimal performance is crucial. A common hurdle that many developers face is when their SQL queries take an excessively long time to execute. In this post, we’ll discuss a particular case where an execution plan indicates overly high costs, and how to effectively optimize that query for better performance. The Problem: An Expensive Execution Plan Consider the following SQL query snippet, which runs indefinitely when executed due to its complex design and costly execution plan: [[See Video to Reveal this Text or Code Snippet]] Upon execution, the generated execution plan shows a staggering cost that can leave developers scratching their heads. The complex EXISTS subquery contributes significantly to the overall cost, making the query unoptimized. Execution Plan Overview Here's a breakdown of what the execution plan reveals: Total Cost: An astronomical figure (825G) indicating poor performance potential. Table Access Full: Several full table scans, which are often a red flag for inefficiency. Temporary Tables: The involvement of temp tables indicates repeated data manipulation tasks, further adding to the execution time. The Solution: Using Window Functions To tackle the issue of performance and make the query simpler, we can employ window functions. Window functions allow operations to be performed over a set of rows that are somehow related to the current row. This approach eliminates the need for a subquery and can significantly enhance responsiveness. The Optimized Query Instead of the intricate structure of the original query, we can simplify it using a single SELECT statement with a window function: [[See Video to Reveal this Text or Code Snippet]] Key Changes Explained Removal of CTEs: The Common Table Expressions (CTEs) have been removed, reducing the query's complexity and simplifying the read. Use of Window Function: The MAX function is applied in conjunction with OVER (PARTITION BY...), which eliminates the need for the EXISTS clause while still achieving the same outcome. Improved Readability: This refactored query is not only easier to write and maintain but also streamlines the logic, ensuring faster execution. Benefits of the Optimized Approach Faster Performance: By using window functions, the database engine can better manage how it reads and processes data, ultimately leading to quicker execution times. Lower Resource Costs: A more efficient query directly translates into reduced resource consumption and lower costs, which is essential for any project managing large datasets. Simplified Maintenance: Simplifying the SQL code helps future-proof your work, making it more comprehensible for others who may work on it later. Conclusion The journey from an inefficient SQL execution plan to an optimized query does not have to be daunting. By understanding the implications of query structure and leveraging powerful SQL features like window functions, you can enhance performance and readability. Always remember: efficient queries not only run better but also support the overall health of your data processing activities. With this knowledge, you’re now better equipped to tackle expensive execution plans and ensure your SQL queries remain both efficient and effective.