Mysql 查询以统计每个经理的员工数（对于经理也是零计数）

经理表：

create table Manager(id integer, name varchar(100));
insert into Manager(id, name) values(1, "M1");
insert into Manager(id, name) values(2, "M2");
insert into Manager(id, name) values(3, "M3");

员工表和经理id（m_id）

已执行的查询：

select M.id, M.name, count(E.id) from Manager as M, Employee as E where E.m_id=M.id group by E.m_id, M.id, M.name;

输出：

1   M1  2
2   M2  1 

预期产出：

1   M1  2
2   M2  1
3   M3  0

---

请帮助我如何将M3经理和分配给他的0员工包括在内？

您应该使用左联接

SELECT M.id, M.name, count(E.id) from Manager as M LEFT JOIN Employee as E ON E.m_id=M.id GROUP BY E.m_id, M.id, M.name;

---

你应该使用左连接

SELECT M.id, M.name, count(E.id) from Manager as M LEFT JOIN Employee as E ON E.m_id=M.id GROUP BY E.m_id, M.id, M.name;