﻿ SQL: List the number of employees and average salary

# SQL Exercise: List the number of employees and average salary

## SQL employee Database: Exercise-104 with Solution

[An editor is available at the bottom of the page to write and execute the scripts.]

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

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous SQL Exercise: Check if all the employees numbers are indeed unique.
Next SQL Exercise: List the names of those employees starting with A.

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.

﻿

## SQL: Tips of the Day

Grouped LIMIT in PostgreSQL: Show the first N rows for each group?

```db=# SELECT * FROM xxx;
id | section_id | name
----+------------+------
1 |          1 | A
2 |          1 | B
3 |          1 | C
4 |          1 | D
5 |          2 | E
6 |          2 | F
7 |          3 | G
8 |          2 | H
(8 rows)
```

I need the first 2 rows (ordered by name) for each section_id, i.e. a result similar to:

```id | section_id | name
----+------------+------
1 |          1 | A
2 |          1 | B
5 |          2 | E
6 |          2 | F
7 |          3 | G
(5 rows)
```

PostgreSQL v9.3 you can do a lateral join

```select distinct t_outer.section_id, t_top.id, t_top.name from t t_outer
join lateral (
select * from t t_inner
where t_inner.section_id = t_outer.section_id
order by t_inner.name
limit 2
) t_top on true
order by t_outer.section_id;
```

Database: PostgreSQL

Ref: https://bit.ly/3AfYwZI

We are closing our Disqus commenting system for some maintenanace issues. You may write to us at reach[at]yahoo[dot]com or visit us at Facebook