Using a
CASE Statement in SQL: Assigning Text Values to Exam Results
As a programmer, it is vital to have a solid understanding of SQL, as it is one of the most widely used programming languages in the world. SQL (Structured Query Language) is a standard language for managing relational databases, and it includes various functions that make it a robust programming tool.
One of those most-used features is the
CASE statement, which is used for conditional programming. One commonly used scenario for a
CASE statement is when you need to assign text values to exam results. In this case, you can use a
CASE statement to assign grades such as “A,” “B,” and “C,” based on a student’s score.
Writing Conditions and Creating an Alias Column
To assign text values to exam results using a
CASE statement in SQL, you first have to understand how to write conditions. Let’s say you have a table of exam results, and you want to assign letter grades based on the score.
You can use a
CASE statement to write conditions like this:
“`
SELECT student_id, exam_name, score,
CASE
WHEN score >= 90 THEN ‘A’
WHEN score >= 80 AND score < 90 THEN 'B'
WHEN score >= 70 AND score < 80 THEN 'C'
WHEN score >= 60 AND score < 70 THEN 'D'
ELSE ‘F’
END AS letter_grade
FROM exam_results;
“`
This code will select the student ID, exam name, score, and then use the
CASE statement to assign a letter grade based on the score. If the score is 90 or above, the student gets an “A,” if it is between 80 and 89, they get a “B,” and so on.
If the score is below 60, they get an “F.” The “AS letter_grade” command creates an alias for the result column, which simplifies the results table by bringing all assigned text values under one column. Solution 1: Non-overlapping Conditions in
CASE
In some cases, you may need to assign non-overlapping conditions to a
CASE statement. For example, you may want to assign “bad”, “average” and “good” results based on a score range.
You would use a non-overlapping
CASE statement that looks like this:
“`
SELECT student_id, exam_name, score,
CASE
WHEN score < 60 THEN 'Bad'
WHEN score >= 60 and score <= 79 THEN 'Average'
ELSE ‘Good’
END AS category
FROM exam_results;
“`
This code assigns a “Bad” result to any score below 60, an “Average” result to any score between 60-79, and a “Good” result to any score above 80.
Using an Alias to Rename the Category Column
As with the previous example, you can use an alias to rename the “category” column to something more meaningful by adding “AS result_category” to the end of the code:
“`
SELECT student_id, exam_name, score,
CASE
WHEN score < 60 THEN 'Bad'
WHEN score >= 60 and score <= 79 THEN 'Average'
ELSE ‘Good’
END AS result_category
FROM exam_results;
“`
This code will produce a results table that includes the student ID, exam name, score, and the category assigned by the
CASE statement. By using an alias, you can give the text value column a more meaningful name, making it easier to read and understand.
Conclusion
In conclusion, using a
CASE statement in SQL is an efficient way of assigning text values to exam results based on conditions. With conditional programming using the
CASE statement, you can assign text values to exam results quickly and efficiently, making it easier for teachers or analysts to analyze the grades quickly and with fewer human errors. Furthermore, the use of an alias means you can rename columns to something user-friendly, making it easier to read and analyze the data.
Overall, learning how to use a
CASE statement in SQL is a valuable skill for any programmer dealing with databases, and it is essential to learn it to manage data effectively. Solution 2: Adding an Additional Condition to the
CASE
In some cases, you may need to add an additional condition to your
CASE statement. For example, you may want to assign an “Average” result to a range of scores (such as 75-80).
You can do this by adding an “AND” operator to the condition:
“`
SELECT student_id, exam_name, score,
CASE
WHEN score >= 90 THEN ‘A’
WHEN score >= 80 AND score < 90 THEN 'B'
WHEN score >= 75 AND score < 80 THEN 'Average'
WHEN score >= 60 AND score < 75 THEN 'C'
ELSE ‘F’
END AS letter_grade
FROM exam_results;
“`
This code assigns an “Average” result to any score between 75-80.
Handling NULL Values Without an ELSE Statement
It is important to note that in some cases, you may have NULL values in your data. In such cases, adding an ELSE statement may not be the best solution.
For example, consider this code:
“`
SELECT student_id, exam_name, score,
CASE
WHEN score >= 90 THEN ‘A’
WHEN score >= 80 AND score < 90 THEN 'B'
WHEN score >= 60 AND score < 80 THEN 'C'
WHEN score IS NULL THEN ‘No Score Available’
END AS letter_grade
FROM exam_results;
“`
This code assigns a “No Score Available” result to any NULL values in the score column. Since there is no ELSE statement, any score that does not meet the above conditions will be assigned NULL, and not “F.”
Solution 3: Using Overlapping Conditions in the
CASE
In some cases, you may want to use overlapping conditions in your
CASE statement. This can be useful if you want to assign a result value based on a range of scores.
Here is an example of how this can be done:
Structuring Overlapping Conditions for the Results:
“`
SELECT student_id, exam_name, score,
CASE
WHEN score >= 90 THEN ‘A’
WHEN score >= 80 THEN ‘B’
WHEN score >= 70 THEN ‘C’
WHEN score >= 60 THEN ‘D’
ELSE ‘F’
END AS letter_grade
FROM exam_results;
“`
This code assigns an “A” result to any score above 90, a “B” result to any score above 80, a “C” result to any score above 70, and so on. Notice that as long as a score meets the requirement of one condition, the code will exit the
CASE statement and assign the corresponding result value.
Simplifying the ELSE Statement
In cases where you do not need to assign text values to result values at various intervals, you can simplify the ELSE statement, as shown below:
“`
SELECT student_id, exam_name, score,
CASE
WHEN score >= 70 THEN ‘Pass’
ELSE ‘Fail’
END AS result
FROM exam_results;
“`
This code assigns a “Pass” result to any score over 70, and a “Fail” result to any score below 70. Since there are no other intervals in between, there is no need for any other conditions.
As long as you structure your conditions correctly, a single statement under the
CASE condition may suffice.
Conclusion
Conditional programming in SQL is essential for programming in databases, and the
CASE statement is one of the most crucial tools at your disposal. By learning to use conditional programming, you can assign text values to exam results based on conditions quickly and efficiently, making it easier for teachers or analysts to analyze the grades quickly and accurately.
With the various solutions presented, you can structure your code correctly, assign text values or result values to the data easily, and handle any NULL values or additional conditions required for your data analysis. Incorporating these techniques with
CASE statements can help you manage data more efficiently and communicate it more effectively in various business contexts. In conclusion, the use of conditional programming in SQL through the
CASE statement is a vital tool for assigning text and result values to exam results based on specific conditions. By understanding how to write conditions, create alias columns and handle NULL values and additional conditions, programmers can manage data more efficiently, saving time and effort in the process.
The use of overlapping and non-overlapping conditions in the
CASE statement can help create more structured conditions for assigning values to results. Overall, learning SQL and its tools effectively is essential for database programming and further professional development.