mysql select后面的子查询

select后面的子查询使用,只能是标量查询

#案例：查询每个部门的员工个数

SELECT d.*,(    SELECT COUNT(*)    FROM employees    WHERE employees.`department_id`=d.department_id)FROM    departments d;

#案例：查询员工号=102的部门名

SELECT department_nameFROM    employees eINNER JOIN    departments dON    e.`department_id`=d.`department_id`WHERE    e.`employee_id`=102;

用子查询

SELECT (SELECT department_nameFROM    employees eINNER JOIN    departments dON    e.`department_id`=d.`department_id`WHERE    e.`employee_id`=102);