Select e.city,Count(Cid),AVG(balance) as CheckingBalance
from customer c
inner join transactions t on t.cid = c.cid
inner join employees e on e.eid = t.eid
inner join accounts a on a.tid = t.tid
Where account_type = 'Checking'
Group by e.city

SELECT e.*,t.CustCnt,t.AvgBal
FROM employees e
INNER JOIN (SELECT c.city,COUNT(DISTINCT c.cid) AS CustCnt, AVG(a.balance*1.0) AS AvgBal
            FROM customer c
            INNER JOIN transactions t
            ON t.cid = c.cid
            INNER JOIN accounts a
            ON a.aid = t.aid
            WHERE a.account_type='Checking'
            GROUP BY c.city
           )t
On t.city = e.city