SELECT bid ,  count(*) FROM Reserves GROUP BY bid
Find the number of reservations for each boat.
create table Sailors (
sid INTEGER primary key,
name TEXT,
rating INTEGER,
age INTEGER
);
CREATE TABLE Boats (
  bid INTEGER primary key,
  name TEXT,
  color TEXT
);
CREATE TABLE Reserves (
  sid INTEGER,
  bid INTEGER,
  day TEXT,
  foreign key (sid) references Sailors(sid),
  foreign key (bid) references Boats(bid)
);
INSERT INTO Sailors VALUES [(1, 'Eugene', 7, 22), (2, 'Luis', 2, 39)]
INSERT INTO Boats VALUES [(101, 'Legacy', 'red'), (102, 'Melon', 'blue')]
INSERT INTO Reserves VALUES [(1, 102, '9/12'), (2, 102, '9/13')]