SQL Exercise: Display the unique department with jobs

Last update on April 18 2023 06:46:27 (UTC/GMT +8 hours)

SQL employee Database: Exercise-10 with Solution

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10. From the following table, write a SQL query to find the unique department with jobs. Return department ID, Job name.

Sample table: employees

Pictorial Presentation:

SQL exercises on employee Database: Display the unique department with jobs

Sample Solution:

SELECT DISTINCT dep_id,
                job_name
FROM employees ;

Sample Output:

 dep_id | job_name
--------+-----------
   3001 | MANAGER
   2001 | ANALYST
   3001 | SALESMAN
   1001 | MANAGER
   1001 | PRESIDENT
   2001 | MANAGER
   2001 | CLERK
   1001 | CLERK
   3001 | CLERK
(9 rows)

Explanation:

The said query in SQL that selects distinct combinations of the dep_id and job_name columns from the 'employees' table. The "DISTINCT" keyword ensures that each combination of dep_id and job_name appears only once in the result set, even if there are multiple employees with the same job and department.

A query like this might be used to get all unique job titles and departments in the company based on the "employees" table.

Relational Algebra Expression:

Relational Algebra Tree:

Practice Online

Sample Database: employee

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Previous SQL Exercise: List employees id, salary, and commission.
Next SQL Exercise: List the employees not in department 2001.

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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

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