avg sql function [closed] - sql

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I have a table employees
EMPLOYEE_ID FIRST_NAME LAST_NAME HIRE_DATE JOB_ID SALARY DEPARTMENT_ID
-------------------------------------------------------------------------------------------
100 Steven King 17-JUN-03 AD_PRES 24000 90
101 Neena Kochhar 21-SEP-05 AD_VP 17000 90
102 Lex De Haan 13-JAN-01 AD_VP 17000 90
103 Alexander Hunold 03-JAN-06 IT_PROG 9000 60
104 Bruce Ernst 21-MAY-07 IT_PROG 6000 60
105 David Austin 25-JUN-05 IT_PROG 4800 60
106 Valli Pataballa 05-FEB-06 IT_PROG 4800 60
107 Diana Lorentz 07-FEB-07 IT_PROG 4200 60
109 Daniel Faviet 16-AUG-02 FI_ACCOUNT 9000 100
110 John Chen 28-SEP-05 FI_ACCOUNT 8200 100
111 Ismael Sciarra 30-SEP-05 FI_ACCOUNT 7700 100
112 Jose Manuel Urman 07-MAR-06 FI_ACCOUNT 7800 100
113 Luis Popp 07-DEC-07 FI_ACCOUNT 6900 100
and table departments
DEPARTMENT_ID DEPARTMENT_NAME
-------------------------------
30 Purchasing
50 Shipping
60 IT
90 Executive
100 Finance
I need to write 3 queries:
Get department name and number of employees in each department sorting ascending
I tried this
select count(e.employee_id), d.department_name
from t_employees e, t_departments d
where d.department_id = e.department_id
group by e.department_name
order by count(e.employee_id);
Not sure if it will work since I can not really try it.
Get department name and average salary where average salary by department is more or equal 5000
Result table
DEPARTMENT_NAME AVERAGE_SALARY
---------------------------------
Executive 19333,333
IT 5760
Finance 7920`
select d.department_name, AVG(e.salary) as AVARAGE_SALARY
from t_departments d, t_employees e
where d.department_id = e.department_id
and avg(e.salary) >= '5000'
group by d.department_name;
Get first name and last name of employees who have salary bigger than the average salary from the department they work in
Result table
FIRST_NAME LAST_NAME
---------------------------------
Steven King
Alexander Hunold
Bruce Ernst
Daniel Faviet
John Chen
I have no code for this one.

Answer 1

You're quite close.
I don't have your tables so I'll use Scott's sample schema. Try to apply it to your data model.
First:
SQL> select d.dname, count(*) cnt
2 from emp e join dept d on e.deptno = d.deptno
3 group by d.dname
4 order by cnt desc;
DNAME CNT
-------------- ----------
SALES 6
RESEARCH 5
ACCOUNTING 3
Second: not where, but having:
SQL> select d.dname, avg(e.sal) avg_sal
2 from emp e join dept d on e.deptno = d.deptno
3 group by d.dname
4 having avg(e.sal) > 2000; --> this
DNAME AVG_SAL
-------------- ----------
ACCOUNTING 2916,66667
RESEARCH 2175
SQL>
Third:
SQL> with avgsal as
2 (select deptno,
3 round(avg(sal), 1) avgsal
4 from emp
5 group by deptno
6 )
7 select e.deptno, e.ename, e.sal, a.avgsal
8 from emp e join avgsal a on a.deptno = e.deptno
9 where e.sal > a.avgsal
10 order by e.deptno;
DEPTNO ENAME SAL AVGSAL
---------- ---------- ---------- ----------
10 KING 5000 2916,7
20 JONES 2975 2175
20 SCOTT 3000 2175
20 FORD 3000 2175
30 ALLEN 1600 1566,7
30 BLAKE 2850 1566,7
6 rows selected.
SQL>