SQL Exercise: List the number of employees and average salary

Last update on December 20 2024 11:40:00 (UTC/GMT +8 hours)

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104. From the following table, write a SQL query to find number of employees and average salary. Group the result set on department id and job name. Return number of employees, average salary, department ID, and job name.

Sample table: employees

Sample Solution:

SELECT count(*),
       avg(salary),
       dep_id,
       job_name
FROM employees
GROUP BY dep_id,
         job_name;

Sample Output:

 count |          avg          | dep_id | job_name
-------+-----------------------+--------+-----------
     1 | 2750.0000000000000000 |   3001 | MANAGER
     2 | 3100.0000000000000000 |   2001 | ANALYST
     4 | 1500.0000000000000000 |   3001 | SALESMAN
     1 | 2550.0000000000000000 |   1001 | MANAGER
     1 | 6000.0000000000000000 |   1001 | PRESIDENT
     1 | 2957.0000000000000000 |   2001 | MANAGER
     2 | 1050.0000000000000000 |   2001 | CLERK
     1 | 1400.0000000000000000 |   1001 | CLERK
     1 | 1050.0000000000000000 |   3001 | CLERK
(9 rows)

Explanation:

The said query in SQL that returns the number of employees, average salary, department ID, and job name for each unique combination of dep_id and job_name from the employees table.

The GROUP BY CLAUSE groups the results by dep_id and job_name columns.

Relational Algebra Expression:

Relational Algebra Tree:

Practice Online

Sample Database: employee

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