SQL Exercise: Departments where more than two employees are working

SQL JOINS: Exercise-29 with Solution

From the following tables write a SQL query to find the names of departments where more than two employees are employed. Return dpt_name.

Sample table: emp_department

DPT_CODE DPT_NAME        DPT_ALLOTMENT
-------- --------------- -------------
      57 IT                      65000
      63 Finance                 15000
      47 HR                     240000
      27 RD                      55000
      89 QC                      75000

Sample table: emp_details

 EMP_IDNO EMP_FNAME       EMP_LNAME         EMP_DEPT
--------- --------------- --------------- ----------
   127323 Michale         Robbin                  57
   526689 Carlos          Snares                  63
   843795 Enric           Dosio                   57
   328717 Jhon            Snares                  63
   444527 Joseph          Dosni                   47
   659831 Zanifer         Emily                   47
   847674 Kuleswar        Sitaraman               57
   748681 Henrey          Gabriel                 47
   555935 Alex            Manuel                  57
   539569 George          Mardy                   27
   733843 Mario           Saule                   63
   631548 Alan            Snappy                  27
   839139 Maria           Foster                  57

Sample Solution:

-- Selecting the department name from the result of an inner join between 'emp_details' and 'emp_department' tables
SELECT emp_department.dpt_name
-- Specifying the tables to retrieve data from ('emp_details' and 'emp_department')
FROM emp_details 
-- Performing an inner join based on the equality of 'emp_dept' in 'emp_details' and 'dpt_code' in 'emp_department'
INNER JOIN emp_department
ON emp_dept = dpt_code
-- Grouping the results by the department name
GROUP BY emp_department.dpt_name
-- Applying a filter to the grouped results, including only those with a count greater than 2
HAVING COUNT(*) > 2;

Output of the Query:

dpt_name
Finance
IT
HR

Explanation:

The said SQL query is selecting the 'dpt_name' column from the emp_department table.
This code is joining the emp_details table with the emp_department table on the matching value in the 'emp_dept' column of the emp_details table and the 'dpt_code' column of the emp_department table.
The query also use GROUP BY clause that groups the result-set by one or more columns.
The HAVING clause is used in conjunction with the GROUP BY clause. It is used to filter groups based on a specified condition, in this case, the condition is COUNT(*) > 2, which means it will only return the groups that have more than 2 rows.
It returns the name of the department whose count of employees is more than 2.

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