SQL Exercise: List the department where at least two employees work

SQL employee Database: Exercise-98 with Solution

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98. From the following table, write a SQL query to identify the departments in which at least two employees are employed. Return department id, number of employees.

Sample table: employees

Sample Solution:

SELECT dep_id,
       count(*)
FROM employees
GROUP BY dep_id
HAVING count(*) >= 2;

Sample Output:

 dep_id | count
--------+-------
   3001 |     6
   1001 |     3
   2001 |     5
(3 rows)

Explanation:

The given query in SQL that retrieves the count of employees in each department, but only for those departments that have two or more employees from the table 'employees'.

It groups the results by the "dep_id" column, and counts the number of records for each unique value of "dep_id".

The HAVING clause filters the results to include only those groups where the count of records is greater than or equal to 2.

Relational Algebra Expression:

Relational Algebra Tree:

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Sample Database: employee

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