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Databases SQL Reporting by Example Day 1: Joining Tables Subjects in the Big Room

Posted by Michael Hill
Michael Hill
3,960 Points

My Solution to this Challenge

After the last challenge I was curious about being more efficient with sub-queries. This was the final code I got that avoided hard coding the room id:

SELECT NAME FROM SUBJECTS WHERE ID IN (SELECT SUBJECT_ID FROM CLASSES
WHERE ROOM_ID = (SELECT ID FROM ROOMS ORDER BY CAPACITY DESC LIMIT 1));

I noticed I didn't need to add a Distinct keyword to exclude the duplicates with this answer. I'm assuming this is because my WHERE statement is technically pulling from a table that only populates each class id once?

1 Answer

Steven Parker
Steven Parker
229,708 Points
Steven Parker
Steven Parker
229,708 Points

The second WHERE actually does return duplicate IDs, but the first WHERE is using the "IN" operator so it doesn't matter how many times a value appears in a result set, only if it exists in it or not.