Revised database queries for individual course page

[zichenzhang04]

Description of the Changes

Revised database queries for individual course page

Type of the Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation change
• Dependency/Package change

Checklist before Submitting:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made necessary corresponding changes (if needed) to the documentation
• My changes generate no new warnings
• I have updated Python requirements.txt and/or JS packages (if needed)

After making the PR, plase check:
You have checked that the program builds successfully on Heroku CI/CD, and
You have thoroughly tested the resulting application on Heroku
Keep up the good work, Collagers!