When it comes to working with SQL Server, there are certain best practices that can help optimize performance and ensure efficient database management. Whether you are a beginner or an experienced SQL Server user, following these practices can greatly enhance your skills and improve the overall performance of your database.

1. Know your data and business application well

It is crucial to familiarize yourself with the data and business application you are working with. Understanding the data volume and distribution in your database will help you make informed decisions and optimize your queries accordingly.

2. Test your queries with realistic data

Testing your queries with realistic data is essential to ensure that they perform well in a production environment. SQL statements tested with unrealistic data may behave differently when used in real-world scenarios. Therefore, it is important to closely resemble the data distribution in your test environment to that in the production environment.

3. Write identical SQL statements in your applications

Take full advantage of stored procedures and functions whenever possible. These precompiled objects offer performance gains and can improve the overall efficiency of your applications.

4. Use indexes on the tables carefully

Creating the necessary indexes on your tables is important for optimizing query performance. However, it is crucial to strike a balance and avoid creating too many indexes, as they can degrade performance.

5. Make an indexed path available

When writing SQL statements, ensure that an indexed path is available to take advantage of indexes. Using SQL hints is one way to ensure that the index is used and query performance is optimized.

6. Understand the Optimizer

Having a good understanding of how the optimizer uses indexes, WHERE clauses, ORDER BY clauses, and HAVING clauses can greatly impact query performance. Take the time to familiarize yourself with the optimizer’s behavior and optimize your queries accordingly.

7. Think globally when acting locally

Any changes you make in the database to tune one SQL statement may affect the performance of other statements used by applications and users. Therefore, it is important to consider the broader impact of your changes and ensure they do not negatively impact other queries.

8. The WHERE clause is crucial

Be mindful of the WHERE clauses you use in your queries. Certain WHERE clauses, such as those using comparison operators like >, >=, <=, or LIKE ‘%pattern%’, may not use the index access path even if an index is available. Understanding these nuances can help you optimize your queries effectively.

9. Use WHERE instead of HAVING for record filtering

Avoid using the HAVING clause along with GROUP BY on an indexed column. Instead, use the WHERE clause for record filtering, as it can improve query performance.

10. Specify the leading index columns in WHERE clauses

For composite indexes, ensure that the leading column of the index is specified in the WHERE clause. This allows the query to use the index effectively and optimize performance.

11. Evaluate index scan vs. full table scan

When selecting a large number of rows from a table, a full table scan is usually faster than an index access path. However, if the percentage of table rows accessed is 15 percent or less, an index scan can work better. Understanding when to use each approach can greatly improve query performance.

12. Use ORDER BY for index scan

If the ORDER BY clause is on an indexed column, the SQL Server optimizer will use an index scan. This can significantly improve query performance when sorting large result sets.

13. Minimize table passes

Reducing the number of table passes in a SQL query can result in better performance. Queries with fewer table passes generally execute faster, so optimize your queries to minimize the number of table passes.

14. Join tables in the proper order

When performing multiple table joins, always start with the most restrictive search first. This filters out the maximum number of rows in the early phases of the join, improving performance in subsequent phases.

15. Redundancy is good in WHERE condition

Provide as much information as possible in the WHERE clause to help the optimizer clearly infer conditions. This redundancy can improve query performance by allowing the optimizer to make more informed decisions.

16. Keep it simple, stupid

Complex SQL statements can overwhelm the optimizer and result in suboptimal performance. Sometimes, writing multiple simpler SQL statements can yield better performance than a single complex SQL statement.

17. You can reach the same destination in different ways

Each SQL statement may use a different access path and perform differently. It is important to explore different approaches and optimize your queries based on their specific requirements.

18. Reduce network traffic and increase throughput

Using T-SQL blocks over multiple SQL statements can achieve better performance and reduce network traffic. Stored Procedures are even better, as they are stored in SQL Server and pre-compiled.

19. Better hardware

Investing in better hardware can significantly improve SQL Server performance. Consider using SCACI drives, RAID 10 arrays, multi-processor CPUs, and a 64-bit operating system to enhance performance.

20. Avoid Cursors

Using SQL Server cursors can result in performance degradation compared to select statements. Whenever possible, try to use correlated subqueries or derived tables for row-by-row operations.

By following these best practices, you can optimize your SQL Server performance, improve query execution times, and enhance the overall efficiency of your database operations.