33. 查詢 employees 表中有多少個部門select count(distinct department_id)from employees 34. 查詢全公司獎金基數的平均值(沒有獎金的人按 0 計算)select avg(nvl(commission_pct, 0))from employees 35. 查詢各個部門的平均工資--錯誤: avg(salary) 返回公司平均工資, 只有一個值; 而 department_id 有多個值, 無法匹配返回select department_id, avg(salary)from employees **在 SELECT 列表中所有未包含在組函數中的列都應該包含在 GROUP BY 子句中--正確: 按 department_id 進行分組select department_id, avg(salary)from employeesgroup by department_id36. Toronto 這個城市的員工的平均工資SELECT avg(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 city = 'Toronto' 37. (有員工的城市)各個城市的平均工資SELECT city, avg(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 city 38. 查詢平均工資高于 8000 的部門 id 和它的平均工資. SELECT department_id, avg(salary) FROM employees e GROUP BY department_id HAVING avg(salary) > 8000 39. 查詢平均工資高于 6000 的 job_title 有哪些SELECT job_title, avg(salary) FROM employees e join jobs j ON e.job_id = j.job_id GROUP BY job_title HAVING avg(salary) > 6000 1. 組函數處理多行返回一行嗎? 是 2. 組函數不計算空值嗎？ 是 3. where子句可否使用組函數進行過濾? 不可以，用having替代 4. 查詢公司員工工資的最大值，最小值，平均值，總和 a) select max(salary),min(salary),avg(salary),sum(salary) b) from employees 5. 查詢各job_id的員工工資的最大值，最小值，平均值，總和 a) select job_id,max(salary),min(salary),avg(salary),sum(salary) b) from employees c) group by job_id 6. 選擇具有各個job_id的員工人數 a) select job_id,count(employee_id) b) from employees c) group by job_id 7. 查詢員工最高工資和最低工資的差距（DIFFERENCE） a) select max(salary),min(salary),max(salary)-min(salary) "DIFFERENCE" b) from employees 8. 查詢各個管理者手下員工的最低工資，其中最低工資不能低于6000，沒有管理者的員工不計算在內 a) select manager_id,min(salary) b) from employees c) where manager_id is not null d) group by manager_id e) having min(salary) >= 6000 9. 查詢所有部門的名字，location_id，員工數量和工資平均值 a) select department_name,location_id,count(employee_id),avg(salary) b) from employees e right outer join departments d c) on e.department_id = d.department_id d) group by department_name,location_id 10. 查詢公司在1995-1998年之間，每年雇用的人數，結果類似下面的格式 total 1995 1996 1997 1998 20 3 4 6 7select count(*) "total",count(decode(to_char(hire_date,'yyyy'),'1995',1,null)) "1995",count(decode(to_char(hire_date,'yyyy'),'1996',1,null)) "1996",count(decode(to_char(hire_date,'yyyy'),'1997',1,null)) "1997",count(decode(to_char(hire_date,'yyyy'),'1998',1,null)) "1998" from employees where to_char(hire_date,'yyyy') in ('1995','1996','1997','1998')

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