SQL Nested Query Homework - sql

Question

Given :
InsuranceCompanies (cid, name, phone, address)
Doctors (did, name, specialty, address, phone, age, cid)
Patients (pid, name, address, phone, age, gender, cid)
Visits (vid, did, pid, date, description)
Where:
cid - Insurance Company code
did - doctor code
pid - patient code
vid - code of visit
And a TASK : Find doctors (did, name) with number of visits (during this year) less than average number of visits to all doctors during this year.
My attempt is:
SELECT D.did, D. name
FROM Doctor D,Visit V
WHERE V.did = D.did and D.did = CV.did and CV.visits <
(SELECT AVG ( CV.visits)
FROM (SELECT V1.did AS did,COUNT(V1.vid) AS visits
FROM Visit V1
WHERE V1.date LIKE '%2012'
GROUP BY V1.did) AS CV)

Answer 1

A BIG THANKS TO Bridge Who shared the most beautifull and user freindly SQL commands visualator ever!
Databse Exemple : http://sqlfiddle.com/#!2/e85c7/3
Solution using views:
CREATE VIEW ThisYear AS
SELECT v.pid,v.vid,v.did
FROM Visits v
WHERE v.date LIKE '%2012';
CREATE VIEW DoctorsVisitCount AS
SELECT v.did, COUNT(v.vid) as c
FROM ThisYear v
GROUP BY v.did;
SELECT DISTINCT d.did,d.dname,dvc.c
FROM Doctors d,DoctorsVisitCount dvc
WHERE dvc.c < (SELECT AVG(dvc.c)
FROM DoctorsVisitCount dvc);