﻿ SQL: Count unique patients who came to examination room C

# SQL Exercise: Count unique patients who came to examination room C

## SQL hospital Database: Exercise-14 with Solution

14. From the following tables, write a SQL query to count the number of unique patients who have been scheduled for examination room 'C'. Return unique patients as "No. of patients got appointment for room C".

Sample table: appointment
``` appointmentid |  patient  | prepnurse | physician |    start_dt_time    |     end_dt_time     | examinationroom
---------------+-----------+-----------+-----------+---------------------+---------------------+-----------------
13216584 | 100000001 |       101 |         1 | 2008-04-24 10:00:00 | 2008-04-24 11:00:00 | A
26548913 | 100000002 |       101 |         2 | 2008-04-24 10:00:00 | 2008-04-24 11:00:00 | B
36549879 | 100000001 |       102 |         1 | 2008-04-25 10:00:00 | 2008-04-25 11:00:00 | A
46846589 | 100000004 |       103 |         4 | 2008-04-25 10:00:00 | 2008-04-25 11:00:00 | B
59871321 | 100000004 |           |         4 | 2008-04-26 10:00:00 | 2008-04-26 11:00:00 | C
69879231 | 100000003 |       103 |         2 | 2008-04-26 11:00:00 | 2008-04-26 12:00:00 | C
76983231 | 100000001 |           |         3 | 2008-04-26 12:00:00 | 2008-04-26 13:00:00 | C
86213939 | 100000004 |       102 |         9 | 2008-04-27 10:00:00 | 2008-04-21 11:00:00 | A
93216548 | 100000002 |       101 |         2 | 2008-04-27 10:00:00 | 2008-04-27 11:00:00 | B
```

Sample Solution:

``````-- SELECTing the count of distinct patients who got appointments for room C
SELECT COUNT(DISTINCT patient) AS "No. of patients got appointment for room C"
-- FROM appointment table
FROM appointment
-- WHERE clause filters appointments for room C
WHERE examinationroom = 'C';
``````

Sample Output:

```No. of patients got appointment for room C
--------------------------------------------
3
(1 row)
```

Explanation:

The said query in SQL that retrieves the number of unique patients who have had appointments in examination room C.

The WHERE statement ensures that only the appointments in examination room C are counted.

Alternative Solution:

Using Subquery in SELECT:

``````
-- SELECTing the count of patients who got appointments for room C using a subquery in SELECT
SELECT (
SELECT COUNT(DISTINCT patient)
FROM appointment
WHERE examinationroom = 'C'
) AS "No. of patients got appointment for room C";
``````

Explanation:

This solution uses a subquery in the SELECT clause to count the number of distinct patients who got appointments for room C.

## Practice Online

E R Diagram of Hospital Database:

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Previous SQL Exercise: Patients and doctors who gave them preliminary care.
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