Which of the following SQL queries correctly finds unmatched rows from students table that have no matching enrollments?

easy📝 Syntax Q3 of 15

SQL - LEFT and RIGHT JOIN

Which of the following SQL queries correctly finds unmatched rows from students table that have no matching enrollments?

ASELECT s.* FROM students s INNER JOIN enrollments e ON s.id = e.student_id WHERE e.student_id IS NULL

BSELECT s.* FROM students s LEFT JOIN enrollments e ON s.id = e.student_id WHERE e.student_id IS NULL

CSELECT s.* FROM students s RIGHT JOIN enrollments e ON s.id = e.student_id WHERE s.id IS NULL

DSELECT s.* FROM students s FULL JOIN enrollments e ON s.id = e.student_id WHERE e.student_id IS NOT NULL

Step-by-Step Solution

Solution:

Step 1: Use LEFT JOIN to keep all students
LEFT JOIN keeps all rows from students and matches from enrollments.
Step 2: Filter students without enrollments
WHERE e.student_id IS NULL selects students with no matching enrollment.
Final Answer:
SELECT s.* FROM students s LEFT JOIN enrollments e ON s.id = e.student_id WHERE e.student_id IS NULL -> Option B
Quick Check:
LEFT JOIN + NULL filter finds unmatched students [OK]

Quick Trick: LEFT JOIN + WHERE right_table.key IS NULL finds unmatched rows [OK]

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