SQL Exercise: Average salary of each commission-based department
29. From the following table, write a SQL query to calculate the average salary of employees who receive a commission percentage for each department. Return department id, average salary.
Sample table: employees+-------------+-------------+-------------+----------+--------------------+------------+------------+----------+----------------+------------+---------------+ | EMPLOYEE_ID | FIRST_NAME | LAST_NAME | EMAIL | PHONE_NUMBER | HIRE_DATE | JOB_ID | SALARY | COMMISSION_PCT | MANAGER_ID | DEPARTMENT_ID | +-------------+-------------+-------------+----------+--------------------+------------+------------+----------+----------------+------------+---------------+ | 100 | Steven | King | SKING | 515.123.4567 | 2003-06-17 | AD_PRES | 24000.00 | 0.00 | 0 | 90 | | 101 | Neena | Kochhar | NKOCHHAR | 515.123.4568 | 2005-09-21 | AD_VP | 17000.00 | 0.00 | 100 | 90 | | 102 | Lex | De Haan | LDEHAAN | 515.123.4569 | 2001-01-13 | AD_VP | 17000.00 | 0.00 | 100 | 90 | | 103 | Alexander | Hunold | AHUNOLD | 590.423.4567 | 2006-01-03 | IT_PROG | 9000.00 | 0.00 | 102 | 60 | | 104 | Bruce | Ernst | BERNST | 590.423.4568 | 2007-05-21 | IT_PROG | 6000.00 | 0.00 | 103 | 60 | | 105 | David | Austin | DAUSTIN | 590.423.4569 | 2005-06-25 | IT_PROG | 4800.00 | 0.00 | 103 | 60 | | 106 | Valli | Pataballa | VPATABAL | 590.423.4560 | 2006-02-05 | IT_PROG | 4800.00 | 0.00 | 103 | 60 | | 107 | Diana | Lorentz | DLORENTZ | 590.423.5567 | 2007-02-07 | IT_PROG | 4200.00 | 0.00 | 103 | 60 | | 108 | Nancy | Greenberg | NGREENBE | 515.124.4569 | 2002-08-17 | FI_MGR | 12008.00 | 0.00 | 101 | 100 | | 109 | Daniel | Faviet | DFAVIET | 515.124.4169 | 2002-08-16 | FI_ACCOUNT | 9000.00 | 0.00 | 108 | 100 | ...... | 206 | William | Gietz | WGIETZ | 515.123.8181 | 2002-06-07 | AC_ACCOUNT | 8300.00 | 0.00 | 205 | 110 | +-------------+-------------+-------------+----------+--------------------+------------+------------+----------+----------------+------------+---------------+
Sample Solution:
-- Selecting 'department_id' and calculating the average salary ('AVG(salary)')
SELECT department_id, AVG(salary)
-- Specifying the table to retrieve data from ('employees')
FROM employees
-- Filtering the results to include only records where 'commission_pct' is not NULL
WHERE commission_pct IS NOT NULL
-- Grouping the results by 'department_id'
GROUP BY department_id;
N.B.: The table's structure has modified for necessary reasons. The query had been utilised for the commission pct column's NULL value.
Sample Output:
department_id | avg
---------------+------------------------
90 | 19333.333333333333
20 | 9500.0000000000000000
100 | 8600.0000000000000000
40 | 6500.0000000000000000
110 | 10150.0000000000000000
80 | 8955.8823529411764706
70 | 10000.0000000000000000
50 | 3475.5555555555555556
60 | 5760.0000000000000000
30 | 4150.0000000000000000
10 | 4400.0000000000000000
0 | 7000.0000000000000000
(12 rows)
Code Explanation:
The said query in SQL that calculates the average salary of employees in each department where the commission percentage is not null. The query will return two columns: "department_id" and the average salary for that department. The query groups the results by "department_id".
Relational Algebra Expression:
Relational Algebra Tree:
Go to:
PREV : Employees who are Sales Representatives or Sales Men.
NEXT : Departments with managers manage more than 4 employees.
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