SQL Missing Marks Rule | Dataford Interview Questions

Your question is SQL Missing Marks Rule. Start with the requirements and the one table on the right.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem

PayPal's analyst training dataset contains one row per student and subject. Before calculating performance metrics, exclude students whose marks are missing in two or more subjects.

Write a PostgreSQL query that returns the students who should remain after this exclusion.

Requirements

Count missing marks separately for each student, where a missing mark is represented by NULL.
Exclude students with missing marks in two or more subjects.
Return each retained student's ID and name, ordered by student_id.

Each student has at most one row per subject, so each NULL mark represents one missing subject mark.

Schema

student_marks

Column	Type	Description
student_id	INT	Student identifier
student_name	VARCHAR(100)	Student's full name
subject_name	VARCHAR(100)	Subject being assessed
marks	NUMERIC(5,2)	Marks earned, or NULL when the mark is missing