SQL Exercise: List the departments where atleast 2 employees work

SQL employee Database: Exercise-102 with Solution

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102. From the following table, write a SQL query to find which departments have at least two employees. Return department name, number of employees.

Sample table: employees

Sample table: department

Sample Solution:

SELECT d.dep_name,
       count(*)
FROM employees e,
     department d
WHERE e.dep_id = d.dep_id
GROUP BY d.dep_name
HAVING count(*) >= 2;

Sample Output:

 dep_name  | count
-----------+-------
 FINANCE   |     3
 MARKETING |     6
 AUDIT     |     5
(3 rows)s

Explanation:

The said query in SQL that selects the "dep_name" and counts the number of rows in each department from the ‘employees’ and 'department' tables that have a matching "dep_id" columns in both the tables.

The WHERE clause includes rows in the result where the "dep_id" in the 'employees' table matches the "dep_id" in the 'department' table.

The HAVING clause only includes the groups where the count of rows is greater than or equal to 2 that is departments that have at least 2 employees.

Relational Algebra Expression:

Relational Algebra Tree:

Practice Online

Sample Database: employee

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