Free SQL Help for Devs, DBAs, and the Curious

In the world of business intelligence, SSRS (SQL Server Reporting Services) is a powerful tool that allows users to create, deploy, and manage reports. One feature of SSRS that is often used, but sometimes misunderstood, is the concept of subreports. Subreports are essentially reports within reports. They allow you to structure your data in a way that's easier to understand and navigate. Yet, while subreports can be incredibly useful, they can also be performance hogs if not optimized properly. In this post, we will discuss some tips and strategies for optimizing SSRS subreports for better performance.

One common mistake that developers make when working with subreports is creating unnecessary complexity. This can happen when a subreport is used to retrieve data that could be retrieved with a single, optimized SQL Server 2016 or 2017 query. For instance, instead of creating a subreport that pulls from multiple tables, consider joining those tables in a single query. Here's an example:

SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
FROM Orders
INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;

Another common issue arises when developers overuse subreports. It's important to remember that every subreport adds an additional query to the total number of queries run to produce the final report. This can quickly add up, particularly in complex reports with many subreports. Thus, consider limiting the use of subreports to situations where they add significant value.

For database administrators working with MySQL 5.7, optimizing the database can significantly improve the performance of SSRS subreports. A well-indexed database can drastically reduce query execution time. Consider creating indexes on the columns that your reports frequently query. Here's a short code snippet that shows how to create an index:

CREATE INDEX idx_customer
ON Customers (CustomerID);

In DB2 11.1, you can improve subreport performance by using the RUNSTATS utility. This utility collects statistics about the data in your database and stores them in the DB2 catalog. These statistics can help the DB2 optimizer choose the most efficient way to execute queries. The following command shows how to use RUNSTATS:

RUNSTATS ON TABLE schema.table 
WITH DISTRIBUTION AND DETAILED INDEXES ALL;

Finally, if you're using Azure SQL, consider leveraging SQL Server Data Tools (SSDT) for optimizing your SSRS subreports. SSDT includes tools for analyzing query performance, which can provide insight into which parts of your subreport are causing performance issues. Additionally, SSDT allows you to test different optimization strategies and see their impact on performance.

Properly optimizing SSRS subreports can greatly improve report generation time and overall performance. It's essential to be aware of the impact that subreports can have on your database server and to take steps to mitigate any negative effects. By following the tips and strategies outlined in this post, you can ensure that your SSRS subreports are both useful and efficient.