SQL Exercise: Physicians, a medical procedure without certification

SQL hospital Database: Exercise-31 with Solution

31. From the following tables, write a SQL query to find all physicians who have performed a medical procedure but are not certified to do so. Return Physician name as "Physician".

Sample table: physician

Sample table: undergoes

Sample table: trained_in

Sample Solution:

SELECT name AS "Physician"
FROM physician
WHERE employeeid IN
    ( SELECT undergoes.physician
     FROM undergoes
     LEFT JOIN trained_In ON undergoes.physician=trained_in.physician
     AND undergoes.procedure=trained_in.treatment
     WHERE treatment IS NULL );

Sample Output:

 Christopher Turk
(1 row)


The said query in SQL retrieves the name of physicians who have not been trained in a particular medical procedure by looking for records in the 'undergoes' table where a corresponding record in the 'trained_in' table with the same physician and procedure does not exist.

From the outer query filters the results by selecting only those records where the "employeeid" column is found in a subquery.

In the subquery the LEFT JOIN keyword joins the 'undergoes' and 'trained_in' tables based on the common columns physician, procedure, and treatment.

The WHERE clause in the subquery filters the results of the join to include only those records where "treatment" is NULL.

Practice Online

E R Diagram of Hospital Database:

E R Diagram: SQL Hospital Database.

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Previous SQL Exercise: Make a report of specified queries.
Next SQL Exercise: Doctors do the same procedure but are not certified.

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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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