子查询练习
子查询应该算是基础篇章的难度天花板了🐳孩怕。。。
1.查询和Zlotkey相同部门的员工姓名和工资
#自古第一题还是不算很难的,直接用子查询就行了
#注意用IN而不是=,万一有多个员工都是叫Zlotkey呢
SELECT department_id,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,工资
#内部查询:查询平均工资
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信息
#使用ALL,大于所有的工资就行啦
SELECT last_name, 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
#需要在部门表中查询部门的id(内查询)
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
#员工表中没有manager_name,但是有manager_id,我们就通过姓名找到领导的id就行了(记住使用IN)
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的信息
#查询最低的工资,查询谁是这个工资
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🤯🤯
首先是用部门进行分组,查询各个部门的平均工资。
然后将得到的数据看作是一张表(因此需要另起别名),使用MIN函数就能得到最低的工资
因为我们需要查询的是部门的信息,然后就根据工资匹配上面求的最低工资就行了,就能够得到部门id
然后查询部门的信息
SELECT MIN(avg_sal) #查询最低工资
FROM (
SELECT AVG(salary) avg_sal #各个部门的平均工资
FROM employees
GROUP BY department_id
) t_dept_avg_sal
#人麻了,隔这套娃呢
SELECT *
FROM departments
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 #各个部门的平均工资
FROM employees
GROUP BY department_id
) t_dept_avg_sal
)
)
#第二种方式
SELECT *
FROM departments
WHERE department_id = (
SELECT department_id
FROM employees
GROUP BY department_id
HAVING AVG(salary) <= ALL(
SELECT AVG(salary) #各个部门的平均工资
FROM employees
GROUP BY department_id
)
)
#查询最低工资部门的方式2(使用LIMIT):
SELECT AVG(salary) avg_sal
FROM employees
GROUP BY department_id
ORDER BY avg_sal ASC
LIMIT 1
上面演示了两种方式,还有两种使用LIMIT确定最高或者最低的方法
9.查询平均工资最低的部门的信息和该部门的平均工资(相关子查询)
前面同第八题一样,多了一个显示平均工资的需求
在最最外层查询信息的一行中查询平均工资,其中部门id从表中得到(注意SQL的执行顺序)
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 #各个部门的平均工资
FROM employees
GROUP BY department_id
) t_dept_avg_sal
)
)
10.查询平均工资最高的job的信息
基本同第八题一样
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
)
)
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
)
)
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 IS NOT NULL
GROUP BY department_id
HAVING AVG(salary) > (
SELECT AVG(salary)
FROM employees
)
12.查询公司中manager的详细信息
#自连接方式:
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
#子查询方式:
SELECT employee_id, last_name, job_id, department_id
FROM employees
WHERE employee_id IN (
SELECT DISTINCT manager_id#查询所有的mgr_id
FROM employees
)
13.各个部门中,按照各自最高工资排序,排名最低的那个部门中的最低工资?
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_sal
)
)
SELECT MIN(salary)
FROM employees
WHERE department_id = (
SELECT department_id
FROM employees
GROUP BY department_id
HAVING MAX(salary) <= ALL(
SELECT max(salary) max_sal
FROM employees
GROUP BY department_id
)
)
14.查询平均工资最高的部门的manager的详细信息(我已经快晕掉了)
SELECT last_name, department_id, email, salary
FROM employees
WHERE employee_id = ANY(
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
)
)
);
15.查询部门的部门号,其中不包括job_id是‘ST_CELRK’的部门号
SELECT department_id
FROM departments
WHERE department_id NOT IN (
SELECT DISTINCT department_id
FROM employees
WHERE job_id = 'ST_CLERK'
)
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'
)