mysql语法问题,判断是否正确

Question

SELECT * from books b
join author a on b.a_id = a.a_id
having a.age < AVG(a.age);

请问我的这个sql语句错在什么地方？

Answer 1

SELECT A.ID, AVG(A.AGE) FROM BOOKS B
JOIN AUTHOR A ON B.A_ID = A.A_ID
GROUP BY A.ID
HAVING A.AGE < AVG(A.AGE);
缺少group by, 和具体所选的列