FAQ: Database Normalization with PostgreSQL - Database Structure and Use (Continued)

This community-built FAQ covers the “Database Structure and Use (Continued)” exercise from the lesson “Database Normalization with PostgreSQL”.

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This exercise can be found in the following Codecademy content:

Design Databases With PostgreSQL

FAQs on the exercise Database Structure and Use (Continued)

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On third step we have the following note:

Note that, because you are grouping by student_id , you will need to aggregate any other column you query; However, because the email column is unique for every student_id , it doesn’t matter how you aggregate. We can, for example, use MIN(email) to get the first email associated with each student_id (and this would yield the same results as MAX(email) ).

Why is it the case that it’s necessary to aggregate the email? seems so weird. Any further explanation?

Yes it seemed weird to me also.
It seems more natural to just add email to the group by command, then to apply a meaningless aggregate function.

Here is the answer they want:
SELECT student_id, SUM(credits_reqd) as total_credits, MIN(email) as student_email
FROM students, students_majors, majors
WHERE students.id = students_majors.student_id
AND students_majors.major_id = majors.id
group by student_id;

Here is what seems a bit more intuitive

SELECT student_id, SUM(credits_reqd) as total_credits, email as student_email
FROM students, students_majors, majors
WHERE students.id = students_majors.student_id
AND students_majors.major_id = majors.id
group by student_id, email;

Are there any speed/accuracy issues we need to be aware of in using the second approach?