Frage im Vorstellungsgespräch bei Google

Pets +------------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | breed | varchar(255) | NO | | NULL | | | acquisition_date | datetime | NO | | NULL | | +------------------+--------------+------+-----+---------+----------------+ Customers +-------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(255) | NO | | NULL | | +-------+--------------+------+-----+---------+----------------+ Sales +-------------+----------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------+----------+------+-----+---------+-------+ | customer_id | int(11) | NO | PRI | NULL | | | pet_id | int(11) | NO | PRI | NULL | | | date | datetime | NO | | NULL | | +-------------+----------+------+-----+---------+-------+ Q1 How many pets of each breed has the shop ever owned?