SQL Exercise: Average salary of each commission-based department
SQL SORTING and FILTERING on HR Database: Exercise-29 with Solution
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
Sample Solution:
SELECT department_id, AVG(salary)
FROM employees
WHERE commission_pct IS NOT NULL
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:
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Query Visualization:
Duration:

Rows:

Cost:

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Previous SQL Exercise: Employees who are Sales Representatives or Sales Men.
Next SQL Exercise: Departments with managers manage more than 4 employees.
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SQL: Tips of the Day
Difference between natural join and inner join
One significant difference between INNER JOIN and NATURAL JOIN is the number of columns returned-
Consider:
TableA TableB +------------+----------+ +--------------------+ |Column1 | Column2 | |Column1 | Column3 | +-----------------------+ +--------------------+ | 1 | 2 | | 1 | 3 | +------------+----------+ +---------+----------+
The INNER JOIN of TableA and TableB on Column1 will return
SELECT * FROM TableA AS a INNER JOIN TableB AS b USING (Column1); SELECT * FROM TableA AS a INNER JOIN TableB AS b ON a.Column1 = b.Column1;
+------------+-----------+---------------------+ | a.Column1 | a.Column2 | b.Column1| b.Column3| +------------------------+---------------------+ | 1 | 2 | 1 | 3 | +------------+-----------+----------+----------+
The NATURAL JOIN of TableA and TableB on Column1 will return:
SELECT * FROM TableA NATURAL JOIN TableB +------------+----------+----------+ |Column1 | Column2 | Column3 | +-----------------------+----------+ | 1 | 2 | 3 | +------------+----------+----------+
Ref: https://bit.ly/3AG5CId
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