SQL Exercise: Find patients without an appointment

SQL hospital Database: Exercise-21 with Solution

21. From the following tables, write a SQL query to find those patients who did not schedule an appointment. Return Patient name as "Patient", Physician name as "Physician" and Medication name as "Medication".

    ssn    |       name        |      address       |  phone   | insuranceid | pcp
-----------+-------------------+--------------------+----------+-------------+-----
 100000001 | John Smith        | 42 Foobar Lane     | 555-0256 |    68476213 |   1
 100000002 | Grace Ritchie     | 37 Snafu Drive     | 555-0512 |    36546321 |   2
 100000003 | Random J. Patient | 101 Omgbbq Street  | 555-1204 |    65465421 |   2
 100000004 | Dennis Doe        | 1100 Foobaz Avenue | 555-2048 |    68421879 |   3

 physician |  patient  | medication |        date         | appointment | dose
-----------+-----------+------------+---------------------+-------------+------
         1 | 100000001 |          1 | 2008-04-24 10:47:00 |    13216584 | 5
         9 | 100000004 |          2 | 2008-04-27 10:53:00 |    86213939 | 10
         9 | 100000004 |          2 | 2008-04-30 16:53:00 |             | 5

 employeeid |       name        |           position           |    ssn
------------+-------------------+------------------------------+-----------
          1 | John Dorian       | Staff Internist              | 111111111
          2 | Elliot Reid       | Attending Physician          | 222222222
          3 | Christopher Turk  | Surgical Attending Physician | 333333333
          4 | Percival Cox      | Senior Attending Physician   | 444444444
          5 | Bob Kelso         | Head Chief of Medicine       | 555555555
          6 | Todd Quinlan      | Surgical Attending Physician | 666666666
          7 | John Wen          | Surgical Attending Physician | 777777777
          8 | Keith Dudemeister | MD Resident                  | 888888888
          9 | Molly Clock       | Attending Psychiatrist       | 999999999

 code |     name     |         brand         | description
------+--------------+-----------------------+-------------
    1 | Procrastin-X | X                     | N/A
    2 | Thesisin     | Foo Labs              | N/A
    3 | Awakin       | Bar Laboratories      | N/A
    4 | Crescavitin  | Baz Industries        | N/A
    5 | Melioraurin  | Snafu Pharmaceuticals | N/A

Sample Solution:

-- SELECTing patient name, physician name, and medication name where appointment is NULL
SELECT t.name AS "Patient",
       p.name AS "Physician",
       m.name AS "Medication"
-- FROM patient table aliased as t
FROM patient t
-- INNER JOIN with prescribes table aliased as s based on patient's SSN
JOIN prescribes s ON s.patient = t.ssn
-- INNER JOIN with physician table aliased as p based on physician's employeeid
JOIN physician p ON s.physician = p.employeeid
-- INNER JOIN with medication table aliased as m based on medication code
JOIN medication m ON s.medication = m.code
-- WHERE clause filters results where appointment is NULL
WHERE s.appointment IS NULL;

Sample Output:

  Patient   |  Physician  | Medication
------------+-------------+------------
 Dennis Doe | Molly Clock | Thesisin
(1 row)

Explanation:

The said query in SQL that selects the names of patients, physicians, and medications for all prescriptions where the appointment is null.

The "JOIN" statement connects the tables 'patient' and 'prescribes' based on the columns ssn and patient, the tables 'prescribes' and 'physician' based on the physician and employeeid columns, and the tables 'prescribes' and 'medication' are based on the columns medication and code.

The "WHERE" clause filters the results to only include prescriptions where the appointment is null.

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E R Diagram of Hospital Database:

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