w3resource

SQL Exercise: Patients with at least one physician appointment

SQL hospital Database: Exercise-4 with Solution

4. From the following table, write a SQL query to count the number of patients who scheduled an appointment with at least one physician. Return count as "Number of patients taken at least one appointment".

Sample table: appointment


Sample Solution: 

SELECT count(DISTINCT patient) AS "No. of patients taken at least one appointment"
FROM appointment;

Sample Output:

 No. of patients taken at least one appointment
------------------------------------------------
                                              4
(1 row)

Explanation:

The given query in SQL that selects the number of distinct patients who have taken at least one appointment from a table 'appointment'.

The uses of COUNT and DISTINCT functions in combination with the patient column counts the number of unique patients in the table.

The query will return only a single row with a single column.

The AS keyword is used to provide a column alias, which renames the column to "No. of patients taken at least one appointment" for easier readability .

Pictorial presentation:

Count the number of patients who booked an appointment with at least one physician

Practice Online


E R Diagram of Hospital Database:

E R Diagram: SQL Hospital Database.

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous SQL Exercise: Physicians who is the head of each department.
Next SQL Exercise: Find the floor and block with a given room number.

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.



Follow us on Facebook and Twitter for latest update.

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

 

We are closing our Disqus commenting system for some maintenanace issues. You may write to us at reach[at]yahoo[dot]com or visit us at Facebook