# FAQ: Subqueries - Comparison Operators

This community-built FAQ covers the "Comparison Operators " exercise from the lesson “Subqueries”.

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## FAQs on the exercise _Comparison Operators _

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Did anyone else begin this section of the lesson only to find that the answer was already filled in?

Why is this valid

``````SELECT *

FROM drama_students

WHERE grade = (SELECT grade from band_students WHERE id = 20);
``````

But this doesn’t return any result

``````SELECT *

FROM drama_students

WHERE grade = (SELECT grade from drama_students WHERE id = 20);
``````

This initially confused me, too.

For the purpose of this exercise, Emlynne is not yet enrolled in drama, so her id ( id = 20) is not listed in the drama_students table.

How come we can’t simply use this SELECT * FROM drama_students WHERE grade = 10; ??

I been asking myself the same question. its more straightforward in this manner.

You can, but it’s a simplified question. The point of the subquery here is that you’re filtering from something located in another table. Think of it like, instead of WHERE grade = 10 it’s WHERE grade = Emlynne Torritti grade from band_students