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SQL Exercise: Physicians who is the head of each department

SQL hospital Database: Exercise-3 with Solution

3. From the following tables, write a SQL query to identify the physicians who are the department heads. Return Department name as “Department” and Physician name as “Physician”.

Sample table: physician


Sample table: department


Sample Solution: 

SELECT d.name AS "Department",
       p.name AS "Physician"
FROM department d,
     physician p
WHERE d.head=p.employeeid;

Sample Output:

    Department    |  Physician
------------------+--------------
 General Medicine | Percival Cox
 Surgery          | John Wen
 Psychiatry       | Molly Clock
(3 rows)

Explanation:

The said query in SQL that selects the "name" column alias as "Department" from the 'department' table and the "name" column alias as "physician" from the 'physician' table, but only for those physicians who are the head of their respective department.

This query uses an implicit join to combine the 'department' and 'physician' tables.

The "WHERE" clause specifies the condition that the "employeeid" of a physician should match the "head" column of their respective department .

Pictorial presentation:

Find the name of the physicians who are the head of each department

Practice Online


E R Diagram of Hospital Database:

E R Diagram: SQL Hospital Database.

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Previous SQL Exercise: Find the nurse who are the head of their department.
Next SQL Exercise: Patients with at least one physician appointment.

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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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