Определить, сколько сотрудников в каждом отделе - MySQL

CREATE TABLE Department(DNumber NUMERIC(5,0) PRIMARY KEY,
DName VARCHAR(30) NOT NULL);
 
CREATE TABLE Topics(TNumber NUMERIC(5,0) PRIMARY KEY,
TName VARCHAR(30) NOT NULL);
 
CREATE TABLE Staff(SNumber NUMERIC(5,0) PRIMARY KEY,
Initials VARCHAR(50) NOT NULL,
POSITION VARCHAR(30) NOT NULL,
Academic_Degrees VARCHAR(30),
Speciality_Code NUMERIC(5,0) NOT NULL,
TNumber NUMERIC(5,0) NOT NULL,
DNumber NUMERIC(5,0) NOT NULL,
FOREIGN KEY(TNumber) REFERENCES Topics,
FOREIGN KEY(DNumber) REFERENCES Department);
 
INSERT INTO Department VALUES(1, 'ddd');
INSERT INTO Department VALUES(2, 'aaaa');
INSERT INTO Department VALUES(3, 'bbbbb');
 
INSERT INTO Topics VALUES(1, 'ssss');
INSERT INTO Topics VALUES(2, 'iii');
INSERT INTO Topics VALUES(3, 'mmmm');
 
INSERT INTO Staff VALUES(1, 'Иванов И.И.', 'looser1', 'noob1',12, 1, 1);
INSERT INTO Staff VALUES(2, 'qw er ty2', 'looser2', 'noob2', 13, 1, 1);
INSERT INTO Staff VALUES(3, 'qw er ty3', 'looser3', 'noob3', 14, 1, 1);
INSERT INTO Staff VALUES(4, 'qw er ty1', 'looser1', 'noob1',12, 1, 1);
INSERT INTO Staff VALUES(5, 'qw er ty2', 'looser2', 'noob2', 13, 2, 2);
INSERT INTO Staff VALUES(6, 'qw er ty3', 'looser3', 'noob3', 14, 3, 3);
 
/* Задание 1 */
SELECT COUNT (*) FROM Staff WHERE DNumber = 1;
SELECT COUNT (*) FROM Staff WHERE DNumber = 2;
SELECT COUNT (*) FROM Staff WHERE DNumber = 3;
/* Задание 2 */
SELECT * FROM Staff WHERE DNumber = 1;
/* Задание 3 */
SELECT * FROM Staff WHERE Initials = 'Иванов И.И.';