07mysql查询语句之子查询

#1.查询和Zlotkey相同部门的员工姓名和工资
SELECT last_name,salary
FROM employees
WHERE department_id IN (
            SELECT department_id
            FROM employees
            WHERE last_name = 'Zlotkey'
);
#2.查询工资比公司平均工资高的员工的员工号，姓名和工资。
SELECT employee_id,last_name,salary
FROM employees
WHERE salary > (
        SELECT AVG(salary)
        FROM employees
);
#3.选择工资大于所有JOB_ID = 'SA_MAN'的员工的工资的员工的last_name, job_id, salary
SELECT last_name,job_id,salary
FROM employees
WHERE salary > ALL(
        SELECT salary
        FROM employees
        WHERE job_id = 'SA_MAN'
        );
#4.查询和姓名中包含字母u的员工在相同部门的员工的员工号和姓名
SELECT employee_id,last_name
FROM employees
WHERE department_id IN (
            SELECT DISTINCT department_id
            FROM employees
            WHERE last_name LIKE '%u%'
);
#5.查询在部门的location_id为1700的部门工作的员工的员工号
SELECT employee_id
FROM employees
WHERE department_id IN (
            SELECT department_id 
            FROM departments
            WHERE location_id = 1700
            );
#6.查询管理者是King的员工姓名和工资
SELECT last_name,salary,manager_id
FROM employees
WHERE manager_id IN (
            SELECT employee_id
            FROM employees
            WHERE last_name = 'King'
            );
#7.查询工资最低的员工信息: last_name, salary

SELECT last_name,salary
FROM employees
WHERE salary =(
        SELECT MIN(salary)
        FROM employees
        );
#8.查询平均工资最低的部门信息
#方式一：
SELECT * ,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal
FROM departments d
WHERE department_id = (
            SELECT department_id
            FROM employees
            GROUP BY department_id
            HAVING AVG(salary) = (
            SELECT MIN(avg_sal)
            FROM (
                SELECT AVG(salary) avg_sal
                FROM employees
                GROUP BY department_id
                ) t_dept_avg_sal
            )

                        );
#方式2：
SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal
FROM departments d
WHERE department_id = (
            SELECT department_id
            FROM employees
            GROUP BY department_id
            HAVING AVG(salary) <= ALL(
                        SELECT AVG(salary) avg_sal
                        FROM employees
                        GROUP BY department_id
                        ) 

                        );
#方式3：LIMIT
SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal
FROM departments d
WHERE department_id = (
            SELECT department_id
            FROM employees
            GROUP BY department_id
            HAVING AVG(salary) =(
                                    SELECT AVG(salary) avg_sal
                        FROM employees
                        GROUP BY department_id
                        ORDER BY avg_sal ASC
                        LIMIT 0,1
                        )
            );
#方式4：
SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal
FROM departments d,(
SELECT department_id,AVG(salary) avg_sal
FROM employees
GROUP BY department_id
ORDER BY avg_sal ASC
LIMIT 0,1
) t_dept_avg_sal
WHERE d.`department_id`= t_dept_avg_sal.department_id
#9.查询平均工资最低的部门信息和该部门的平均工资（相关子查询）
#方式1：
SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal
FROM departments d
WHERE department_id = (
            SELECT department_id
            FROM employees
            GROUP BY department_id
            HAVING AVG(salary) = (
            SELECT MIN(avg_sal)
            FROM (
                SELECT AVG(salary) avg_sal
                FROM employees
                GROUP BY department_id
                ) t_dept_avg_sal
            )

                        );
#10.查询平均工资最高的 job 信息
#方式1：
SELECT *
FROM jobs
WHERE job_id = (
SELECT job_id
FROM employees
GROUP BY job_id
HAVING AVG(salary) = (
            SELECT MAX(avg_sal)
            FROM (
                SELECT AVG(salary) avg_sal
                FROM employees
                GROUP BY job_id
                ) t_job_avg_sal
                      )
);

#方式2：
SELECT *
FROM jobs
WHERE job_id = (
SELECT job_id
FROM employees
GROUP BY job_id
HAVING AVG(salary) >= ALL (
            SELECT AVG(salary) 
            FROM employees
            GROUP BY job_id
                      )
);
#方式3：
SELECT *
FROM jobs
WHERE job_id = (
SELECT job_id
FROM employees
GROUP BY job_id
HAVING AVG(salary) = (
            SELECT MAX(avg_sal)
            FROM (
                SELECT AVG(salary) avg_sal
                FROM employees
                GROUP BY job_id
                ORDER BY avg_sal DESC
                LIMIT 0,1
                ) t_job_avg_sal
                      )
);

#方式4：
SELECT j.*
FROM jobs j,(
SELECT job_id,AVG(salary) avg_sal
FROM employees
GROUP BY job_id
ORDER BY avg_sal DESC
LIMIT 0,1
) t_job_avg_sal
WHERE j.job_id = t_job_avg_sal.job_id
#11.查询平均工资高于公司平均工资的部门有哪些?
SELECT department_id
FROM employees
WHERE department_id
GROUP BY department_id
HAVING AVG(salary) > (
            SELECT AVG(salary)
            FROM employees
            );
#12.查询出公司中所有 manager 的详细信息

#方式1：自连接
SELECT DISTINCT mgr.employee_id,mgr.last_name,mgr.job_id,mgr.department_id
FROM employees emp JOIN employees mgr
ON emp.`manager_id` =mgr.`employee_id`
#方式二：子查询
SELECT employee_id,last_name,job_id,department_id
FROM employees
WHERE employee_id IN (
            SELECT DISTINCT manager_id
            FROM employees
            );
#方式三：使用EXISTS
SELECT employee_id,last_name,job_id,department_id
FROM employees e1
WHERE EXISTS (
        SELECT *
        FROM employees e2
        WHERE e1.`employee_id` = e2.`employee_id`
        );

#13.各个部门中 最高工资中最低的那个部门的 最低工资是多少?
#方式一：
SELECT MIN(salary)
FROM employees
WHERE department_id = (
            SELECT department_id
            FROM employees
            GROUP BY department_id
            HAVING MAX(salary) = (
                        SELECT MIN(max_sal)
                        FROM (
                        SELECT MAX(salary) max_sal
                        FROM employees
                        GROUP BY department_id
                        ) t_dept_max_salary)
);
#方式2：
SELECT MIN(salary)
FROM employees
WHERE department_id = (
            SELECT department_id
            FROM employees
            GROUP BY department_id
            HAVING MAX(salary) <=ALL (
                        SELECT MAX(salary)
                        FROM employees
                        GROUP BY department_id
                        )
);
#方式3：
SELECT MIN(salary)
FROM employees
WHERE department_id = (
            SELECT department_id
            FROM employees
            GROUP BY department_id
            HAVING MAX(salary) = (
                        SELECT MAX(salary) max_sal
                        FROM employees
                        GROUP BY department_id
                        ORDER BY max_sal ASC
                        LIMIT 0,1
                        )
            );
#方式4：
SELECT MIN(salary)
FROM employees e,(
          SELECT department_id,MAX(salary) max_sal
          FROM employees
          GROUP BY department_id
          ORDER BY max_sal ASC
          LIMIT 0,1
          ) t_dept_max_sal
WHERE e.department_id = t_dept_max_sal.department_id
#14.查询平均工资最高的部门的 manager 的详细信息: last_name, department_id, email, salary
#方式1：
SELECT last_name,department_id,email,salary
FROM employees
WHERE employee_id IN (
            SELECT DISTINCT manager_id
            FROM employees
            WHERE department_id = (SELECT department_id
                        FROM employees
                        GROUP BY department_id
            HAVING AVG(salary) = (
                        SELECT MAX(avg_sal)
                        FROM (
                        SELECT AVG(salary) avg_sal
                        FROM employees
                        GROUP BY department_id
                              )t_dept_avg_sal
                        ))
            

);
#方式2：
SELECT last_name,department_id,email,salary
FROM employees
WHERE employee_id IN (
            SELECT DISTINCT manager_id
            FROM employees
            WHERE department_id = (SELECT department_id
                        FROM employees
                        GROUP BY department_id
            HAVING AVG(salary) >=ALL (
                        SELECT AVG(salary) avg_sal
                        FROM employees
                        GROUP BY department_id
                              )
                        )
            

);

#方式3:
SELECT last_name,department_id,email,salary
FROM employees
WHERE employee_id  IN (
            SELECT DISTINCT manager_id
            FROM employees e,(
                      SELECT department_id,AVG(salary) avg_sal
                      FROM employees
                      GROUP BY department_id
                      ORDER BY avg_sal DESC
                      LIMIT 0,1
                     ) t_dept_avg_sal
WHERE e.`department_id` = t_dept_avg_sal.department_id
);
#15. 查询部门的部门号，其中不包括job_id是"ST_CLERK"的部门号
#方式1:
SELECT department_id
FROM departments
WHERE department_id NOT IN(
                SELECT DISTINCT department_id
                FROM employees
                WHERE job_id = 'ST_CLERK'
);
#方式2：
SELECT department_id
FROM departments d
WHERE NOT EXISTS (
        SELECT *
        FROM employees e
        WHERE d.`department_id` = e.`department_id`
        AND e.`job_id` = 'ST_CLERK'
        );
#16. 选择所有没有管理者的员工的last_name

SELECT last_name
FROM employees e1
WHERE NOT EXISTS (
        SELECT *
        FROM employees e2
        WHERE e1.`manager_id` = e2.`employee_id`
);
#17．查询员工号、姓名、雇用时间、工资，其中员工的管理者为 'De Haan'
#方式1：
SELECT employee_id,last_name,hire_date,salary
FROM employees
WHERE manager_id IN (
            SELECT employee_id
            FROM employees
            WHERE last_name = 'De Haan' 
);
#方式2：
SELECT employee_id,last_name,hire_date,salary
FROM employees e1
WHERE EXISTS (
        SELECT *
        FROM employees e2
        WHERE e1.manager_id = e2.employee_id
        AND e2.last_name = 'De Haan'
        );
#18.查询各部门中工资比本部门平均工资高的员工的员工号, 姓名和工资（相关子查询）
#方式1：使用相关子查询
SELECT last_name,salary,department_id
FROM employees e1
WHERE salary > (
        SELECT AVG(salary)
        FROM employees e2
        WHERE department_id = e1.`department_id`

);

#方式2：在from中声明子查询
SELECT e.last_name,e.salary,e.department_id
FROM employees e,(
SELECT department_id,AVG(salary) avg_sal
FROM employees
GROUP BY department_id) t_dept_avg_sal
WHERE e.department_id = t_dept_avg_sal.department_id
AND e.salary > t_dept_avg_sal.avg_sal
#19.查询每个部门下的部门人数大于 5 的部门名称（相关子查询）
SELECT department_name
FROM departments d
WHERE 5 < (
       SELECT COUNT(*)
       FROM employees e
       WHERE d.department_id = e.`department_id`
       );
#20.查询每个国家下的部门个数大于 2 的国家编号（相关子查询）

SELECT * FROM locations;

SELECT country_id
FROM locations l
WHERE 2 < (
       SELECT COUNT(*)
       FROM departments d
       WHERE l.`location_id` = d.`location_id`
       );
       
/*
子查询的编写技巧（或步骤）：①从里往外写 ②从外往里写

如何选择？
①如果子查询相对简单，建议从外往里写。一单子查询结构较复杂，则建议从里往外写
②如果是相关子查询的话，通畅都是从外往里写
*/