How to Calculate an Average from Row Results in Oracle SQL

Learn how to effectively calculate average values for specific columns in Oracle SQL, complete with example queries and detailed explanations.
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How to Calculate an Average from Row Results in Oracle SQL

Calculating averages in SQL can be essential for data analysis, especially when working with a large dataset. If you're using Oracle SQL and need to compute the average from a result set filtered by specific criteria, you might find yourself wondering how to do it effectively. In this post, we will walk you through the steps to achieve this and provide you with a comprehensive SQL query example.

The Initial Setup

Suppose you have a scenario where you want to gather data about students, including the total number of classes they attended and the number of classes in a specific room (let’s call it Room 1001 for Math classes). With the following initial query, you get a dataset like this:

[[See Video to Reveal this Text or Code Snippet]]

However, you want to compute the average across these results after removing the lower-performing students (in this case, Matt and Jane). Your goal is to modify your dataset to include the average total and average Math scores for the remaining users.

Solution: Using Window Functions

To achieve your desired dataset, we can utilize window functions in SQL. This allows us to compute averages without needing complex subqueries. Here’s how you can construct your query:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Query

Inner Query:

The inner query calculates the TOTAL and MATH for each student.

The GROUP BY clause groups results by the USERNAME.

Window Functions:

AVG(A.TOTAL) OVER () computes the average across all totals from the user data.

AVG(A.MATH) OVER () calculates the average Math scores across the valid results.

Filtering:

The WHERE A.TOTAL > 20 condition filters out any students with a total count of classes attended less than or equal to 20. This is your mechanism to exclude the lower-performing students (e.g., Matt and Jane).

Sorting:

Finally, ORDER BY A.TOTAL DESC will ensure the output is sorted in descending order based on the total classes attended.

Final Thoughts

By using window functions, you can simplify your SQL queries while still achieving the desired outcomes. You'll be able to get averages without needing additional sub-queries or complex calculations, resulting in cleaner code and improved performance. This method is efficient and scalable, ensuring your solution can handle larger datasets with ease.

Feel free to adapt the query according to your specific business needs, and happy querying!