How many accounts in North Bohemia has made a transaction with the partner's bank being AB?
A3 contains the region names; North Bohemia is a region.
SELECT COUNT(T2.account_id) FROM district AS T1 INNER JOIN account AS T2 ON T1.district_id = T2.district_id INNER JOIN trans AS T3 ON T2.account_id = T3.account_id WHERE T3.bank = 'AB' AND T1.A3 = 'north Bohemia'