SQL queries can be an essential component of application development, custom reports, and other solutions, but they can also cause lags in your application or report refreshes if they’re not optimized.
Here are five ways to make sure your SQL queries aren’t slowing you down.
1. Review the Execution Plan
Execute your SQL query in SQL Server Management Studio and enable the “show execution plan option.” Then review the execution plan to determine the steps in your SQL query that use table scans rather than indexes or are consuming a large percentage of the overall execution time. This will allow you to determine opportunities for performance gains.
2. Add Indexes
Ensuring all joins are leveraging indexes, with a focus on table scans identified in the previous step, will help maximize query performance. You should also consider adding indexes for tables and columns used in the where clause in addition to joins. Additionally, the SQL Server index tuning wizard can be leveraged to provide baseline recommendations for net new indexes to be created.
3. Optimize Your SQL Structure and Joins
To maximize join performance, you should try to join on data types such as integers rather than text-based data types such as varchar or nvarchar. You can also leverage in-code controls such as FOR and WHILE loops rather than cursors in your query structure, and make sure to limit subqueries to the specific data required.
4. Eliminate Unnecessary Data
As table sizes grow, performance will degrade even if you’ve already put indexes in play. It’s a good idea to have a proper data archival strategy in place to avoid gradual slowdowns over time. Also, make sure to only select the columns you need rather than select everything from every table, so you don’t lose performance scanning data you won’t need.
5. Analyze Your Server Specifications and Performance
Along with data archival strategy, you should also have a database maintenance plan in place with a specific focus on index management and database/log file reduction. Your database server also has to have adequate RAM to support recent versions of SQL Server, so you’ll need at least 16 gigs although 24 gigs would be recommended. Even if you have 24 gigs, check periodically to ensure SQL Server is not taking up more RAM than is needed. Finally, make sure your SSIS ETL processes are running on an ETL or staging server if they are memory/CPU intensive for long periods of time.
Following these basic steps should help improve your overall SQL query performance and keep your reports and applications fast and responsive.
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