27. Patient Appointment No Shows

Problem

Table: Appointments


+----------------+---------+
| Column Name    | Type    |
+----------------+---------+
| appointment_id | int     |
| patient_id     | int     |
| doctor_id      | int     |
| appointment_date | date  |
| status         | enum    |
+----------------+---------+
appointment_id is the primary key (column with unique values) for this table.
patient_id is the ID of the patient who has the appointment.
doctor_id is the ID of the doctor with whom the appointment is booked.
appointment_date is the date when the appointment is scheduled.
status is an ENUM (category) of type ('Completed', 'Cancelled', 'No-Show').

Problem Definition

Write a solution to find the number of times each patient missed their appointments (status = ‘No-Show’).

The result should include the patient_id along with the count of missed appointments as no_shows. If a patient has never missed an appointment, their record should not appear in the output.

Return the result table ordered by patient_id in ascending order.

Example


Input: 
Appointments table:
+----------------+------------+-----------+------------------+----------+
| appointment_id | patient_id | doctor_id | appointment_date | status   |
+----------------+------------+-----------+------------------+----------+
| 1              | 1          | 101       | 2020-09-01       | Completed|
| 2              | 2          | 102       | 2020-09-01       | No-Show  |
| 3              | 1          | 103       | 2020-09-02       | Cancelled|
| 4              | 3          | 101       | 2020-09-02       | No-Show  |
| 5              | 2          | 103       | 2020-09-03       | No-Show  |
| 6              | 3          | 102       | 2020-09-03       | Completed|
+----------------+------------+-----------+------------------+----------+


Output: 
+------------+----------+
| patient_id | no_shows |
+------------+----------+
| 2          | 2        |
| 3          | 1        |
+------------+----------+

Try It Yourself

Database Exercise

Database Schema:


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Exercise Script:


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Available actions: Execute

Solution

To solve this problem, we use SQL queries to analyze the Appointments table and calculate the number of times each patient missed their appointments (where status = ‘No-Show’).

The solution involves using the WHERE clause to filter the Appointments table records where the status is ‘No-Show’. The COUNT function is then applied to count the number of ‘No-Show’ appointments for each patient_id.

The results are grouped by patient_id using the GROUP BY clause to ensure that the count is calculated for each patient individually. Finally, the ORDER BY clause is employed to sort the resulting records by patient_id in ascending order, as specified in the problem statement.


SELECT patient_id,
       COUNT(*) AS no_shows
FROM   Appointments
WHERE  status = 'No-Show'
GROUP  BY patient_id
ORDER  BY patient_id ASC;

Let’s break down the query step by step:

Step 1: Filtering ‘No-Show’ Appointments

We filter out the records in the Appointments table where the status column is ‘No-Show’.


WHERE status = 'No-Show'

Step 2: Grouping by Patient ID

We group the results by patient_id to calculate the count of ‘No-Show’ appointments for each patient.


GROUP BY patient_id

Step 3: Counting ‘No-Show’ Appointments for Each Patient

We apply the COUNT function to count the number of ‘No-Show’ appointments for each patient.


COUNT(*) AS no_shows

Step 4: Ordering the Result

Finally, we order the results by patient_id in ascending order to comply with the problem statement.


ORDER BY patient_id ASC

Final Output:


+------------+----------+
| patient_id | no_shows |
+------------+----------+
| 2          | 2        |
| 3          | 1        |
+------------+----------+

This final result table lists each patient along with the number of appointments they missed, sorted by the patient ID.