Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE Highschooler (id VARCHAR); CREATE TABLE Friend (student_id VARCHAR); CREATE TABLE Highschooler (grade INTEGER, id VARCHAR)
### Question:
Find the average grade of all students who have some friends.
### Answer:
SELECT AVG(grade) FROM Highschooler WHERE id IN (SELECT T1.student_id FROM Friend AS T1 JOIN Highschooler AS T2 ON T1.student_id = T2.id)