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SQL Exercise: Providers of primary care who are not department heads

SQL hospital Database: Exercise-39 with Solution

39. From the following table, write a SQL query to identify those patients whose primary care is provided by a physician who is not the head of any department. Return Patient name as "Patient", Physician Name as "Primary care Physician".

Sample table: patient


Sample table: department


Sample table: physician


Sample Solution:

SELECT pt.name AS "Patient",
       p.name AS "Primary care Physician"
FROM patient pt
JOIN physician p ON pt.pcp=p.employeeid
WHERE pt.pcp NOT IN
    (SELECT head
     FROM department);

Sample Output:

      Patient      | Primary care Physician
-------------------+------------------------
 John Smith        | John Dorian
 Grace Ritchie     | Elliot Reid
 Random J. Patient | Elliot Reid
 Dennis Doe        | Christopher Turk
(4 rows)

Explanation: The said query in SQL that selects the names of patients and their physicians who are not heads of any department.

The JOIN statement combines the 'patient' and 'physician' tables based on the pcp and employeeid columns.

The WHERE clause filters the results to ensure that only pcp's who are not department heads and this is accomplished using a subquery. The subquery that selects the "head" column from the 'department' table and filters out any pcp's who match this value using the NOT IN operator.

Practice Online


E R Diagram of Hospital Database:

E R Diagram: SQL Hospital Database.

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Previous SQL Exercise: Names of all patients who had at least 2 appointments.
Next SQL Exercise: SQL Exercises, Practice, Solution - exercises on employee Database

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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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