Table schema:
CREATE TABLE Highschooler (id VARCHAR); CREATE TABLE Friend (student_id VARCHAR); CREATE TABLE Highschooler (grade INTEGER, id VARCHAR)

Question: Find the minimum grade of students who have no friends.
SQL: SELECT MIN(grade) FROM Highschooler WHERE NOT id IN (SELECT T1.student_id FROM Friend AS T1 JOIN Highschooler AS T2 ON T1.student_id = T2.id)