How to Use the CASE Statement in SQL Server to Classify Student Exam Scores

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Description

Learn how to implement the `CASE` statement in SQL Server to categorize student exam scores into First Class, Second Class, and Third Class efficiently.
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This video is based on the question https://stackoverflow.com/q/65108185/ asked by the user 'snadell' ( https://stackoverflow.com/u/14535737/ ) and on the answer https://stackoverflow.com/a/65108273/ provided by the user 'Tim Biegeleisen' ( https://stackoverflow.com/u/1863229/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding SQL Server Case Statements in Select Clause

When dealing with student performance data, it is essential to evaluate their scores effectively. In SQL Server, the CASE statement is a powerful tool that allows database administrators and developers to categorize data dynamically based on specified conditions.

The Problem Statement

Imagine you have a database containing records of students and their respective scores in multiple exams. Here's a snapshot of what that data looks like:

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

You want to group these scores based on performance criteria:

First Class: Scores above 80%

Second Class: Scores between 60% and 80%

Third Class: Scores below 60%

Your goal is to produce a summary table that shows how many times each student hits each performance category, ultimately looking like this:

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The Solution

To solve this problem, we can utilize conditional aggregation along with the CASE statement in SQL Server. Let’s break down how we can achieve this.

1. Basic SQL Structure

Start with a standard SQL query by selecting data from the relevant tables. In this case, you'll be joining the Student and Marks tables.

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2. Implementing Conditional Aggregation

Here, we use COUNT combined with CASE statements to categorize and count the scores:

FirstClass: Count instances where PercentageScored is greater than 80.

SecondClass: Count instances where scores are between 60 and 80.

ThirdClass: Count instances where scores are less than or equal to 60.

The SQL query will look like this:

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3. Final Query

Here is the complete query that integrates all these components:

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

4. Explanation of Key Components

INNER JOIN: This ensures that only active students from the specified group are included.

WHERE Clause: Filters the data based on student attributes (group and active status).

GROUP BY: Aggregates data based on StudentId, generating a summary per student.

Conclusion

Using the CASE statement along with conditional aggregation in SQL Server allows you to categorize and summarize student scores efficiently. By implementing this approach, you can easily analyze students' performance and derive valuable insights from your data.

Feel free to adapt this query based on your actual database schema and requirements. With this guide, you are now equipped to handle similar data grouping tasks in SQL Server confidently!