Выборка из трех таблиц с функцией count() - C# - Ответ 7575830

CREATE TABLE office(id_office INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, 
address TEXT NOT NULL, email TEXT NOT NULL);
 
CREATE TABLE manager(id_manager INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, 
FIO TEXT NOT NULL, id_office INTEGER NOT NULL, FOREIGN KEY(id_office) REFERENCES office (id_office));
 
CREATE TABLE selling(id_selling INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, 
DATE TEXT NOT NULL,amount INTEGER NOT NULL,
sum_of_sale INTEGER NOT NULL,comment TEXT ,
number_of_disk INTEGER NOT NULL, id_goods INTEGER NOT NULL,
id_manager INTEGER NOT NULL, FOREIGN KEY(id_goods) REFERENCES goods(id_goods),
FOREIGN KEY(id_manager) REFERENCES manager(id_manager));

SELECT  o.id_office AS io, o.address, 
       COUNT(selling.id_selling) 
       FROM office AS o
       JOIN selling 
       ON selling.id_manager = (SELECT manager.id_manager FROM manager WHERE
       manager.id_office=io)  GROUP BY o.address;