SQL Exercise: List the number of employees in each department

Last update on October 09 2025 12:42:29 (UTC/GMT +8 hours)

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101. From the following table, write a SQL query to identify departments with fewer than four employees. Return department ID, number of employees.

Sample table: employees

Sample Solution:

SELECT dep_id,
       count(*)
FROM employees
GROUP BY dep_id
HAVING count(*)<4;

Sample Output:

 dep_id | count
--------+-------
   1001 |     3
(1 row)

Explanation:

The said query in SQL that retrieves the "dep_id" column and counts the number of rows in the 'employees' table for each unique "dep_id".

The HAVING clause include only those groups where the count of rows is less than 4.

Relational Algebra Expression:

Relational Algebra Tree:

Go to:

PREV : Display department, grade, and number of SALESMEN.
NEXT : List the departments where atleast 2 employees work.

Practice Online

Sample Database: employee

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