Question

At the moment I have this

SELECT
    COUNT (enrollment_id) AS enrollments,
    COUNT (result) AS 
    MAX (result) AS highest_result,
    AVG (result) AS average_result,
    MIN (period_code) AS earliest_enrollment    
FROM 
    enrollment
WHERE
result IS NULL  

What I want to have is the number of enrollments in total, which is what COUNT(enrollment_id) is for. I then want to count the number of NULL values in the results column to obtain a column for unfinalised_enrollments.

Will the WHERE clause at the bottom affect the other SELECT statements that use the results column? If so how do I make it so that I can COUNT just the number of NULL values in the results column and display it in a column called unfinalised_enrollment.

thanks in advance.

Answer 1

You can use SUM instead of COUNT:

SELECT
    COUNT (enrollment_id) AS enrollments,
    SUM (CASE WHEN result IS NULL THEN 1 ELSE 0 END) AS null_results,
    MAX (result) AS highest_result,
    AVG (result) AS average_result,
    MIN (period_code) AS earliest_enrollment    
FROM enrollment