Oracle-查询-分组函数练习

分组函数不能在where关键字后面使用

分组函数自动忽略空值

-- 查询 employees 表中有多少个部门
SELECT e.department_id
FROM employees e
WHERE e.department_id IS NOT NULL
GROUP BY e.department_id;
-- HAVING e.department_id IS NOT NULL;

-- 查询全公司奖金基数的平均值(没有奖金的人按 0 计算)
SELECT AVG(NVL(e.commission_pct,0))
FROM employees e
-- 结果为：0.0728971962616822
SELECT AVG(e.commission_pct)
FROM employees e;
-- 结果为：0.222857142857143

-- 查询各个部门的平均工资
SELECT e.department_id,AVG(e.salary)
FROM employees e
WHERE e.department_id IS NOT NULL
GROUP BY e.department_id

-- Toronto这个城市的员工的平均工资
SELECT AVG(e.salary)
FROM employees e
JOIN departments d
ON e.department_id = d.department_id
JOIN locations l
ON d.location_id = l.location_id
WHERE l.city = 'Toronto'
-- GROUP BY l.city

-- (有员工的城市)各个城市的平均工资
SELECT l.city,AVG(e.salary)
FROM employees e
JOIN departments d
ON e.department_id = d.department_id
JOIN locations l
ON d.location_id = l.location_id
GROUP BY l.city

-- 查询平均工资高于 8000 的部门 id 和它的平均工资
SELECT e.department_id,AVG(e.salary)
FROM employees e
GROUP BY e.department_id
HAVING AVG(e.salary) > 8000;

-- 查询平均工资高于 6000 的 job_title 有哪些
SELECT j.job_title,AVG(e.salary)
FROM employees e
JOIN jobs j 
ON e.job_id = j.job_id
GROUP BY j.job_title
HAVING AVG(e.salary) > 6000;

-- 查询各个管理者手下员工的最低工资，其中最低工资不能低于6000，没有管理者的员工不计算在内
SELECT  m.employee_id,MIN(e.salary) min_sal
FROM employees e
JOIN employees m
ON e.manager_id = m.employee_id
GROUP BY m.employee_id
HAVING MIN(e.salary) > 6000

-- 谁的工资比 Abel 高?
SELECT e.last_name,e.salary
FROM employees e
WHERE e.salary > (
                 SELECT emp.salary
                 FROM employees emp
                 WHERE emp.last_name = 'Abel'
               );

-- 查询所有部门的名字，location_id，员工数量和工资平均值
SELECT e.department_id,d.location_id,COUNT(*) emp_num,AVG(e.salary)
FROM employees e
JOIN departments d
ON e.department_id = d.department_id
GROUP BY e.department_id,d.location_id

Oracle-查询-分组函数练习

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