If you see these, stop and rethink.
phone1, phone2, phone3...
Linking tables by name, not ID
One table storing students AND teachers
Half the cells are empty
Your nose knows. Trust the smell.
SQL is obedient. It will run your bad design without complaint.
Your CREATE TABLE statements execute. No errors. Looks good!
Duplicate data, missing records, calculations don't match reality.
Data corruption discovered. Fix requires rewriting half the system.
"If your ERD is wrong, SQL will lie to you."
SQL has no conscience. It executes what you wrote, not what you meant.
You should now be able to do these confidently:
"Week 2 was about structure.
Week 3 will be about retrieval.
You cannot retrieve well
from a structure that lies."
Week 2 Complete
Tables, Keys, Relations
Week 3 Coming
JOINs, Queries
Week 4 Coming
Aggregation, Reports
Before: "I need to store some data"
After: "What are the entities? What are their relationships? What are the keys?"
This mindset is your superpower.
Week 3: JOINs → Week 4: Analysis → Week 5: Mastery