LeetCode-in-Java
3586. Find COVID Recovery Patients
Medium
Table: patients
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| patient_id | int |
| patient_name| varchar |
| age | int |
+-------------+---------+
patient_id is the unique identifier for this table.
Each row contains information about a patient.
Table: covid_tests
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| test_id | int |
| patient_id | int |
| test_date | date |
| result | varchar |
+-------------+---------+
test_id is the unique identifier for this table.
Each row represents a COVID test result. The result can be Positive, Negative, or Inconclusive.
Write a solution to find patients who have recovered from COVID - patients who tested positive but later tested negative.
- A patient is considered recovered if they have at least one Positive test followed by at least one Negative test on a later date
- Calculate the recovery time in days as the difference between the first positive test and the first negative test after that positive test
- Only include patients who have both positive and negative test results
Return the result table ordered by recovery_time in ascending order, then by patient_name in ascending order.
The result format is in the following example.
Example:
Input:
patients table:
+------------+--------------+-----+
| patient_id | patient_name | age |
+------------+--------------+-----+
| 1 | Alice Smith | 28 |
| 2 | Bob Johnson | 35 |
| 3 | Carol Davis | 42 |
| 4 | David Wilson | 31 |
| 5 | Emma Brown | 29 |
+------------+--------------+-----+
covid_tests table:
+---------+------------+------------+--------------+
| test_id | patient_id | test_date | result |
|---------|------------|------------|--------------|
| 1 | 1 | 2023-01-15 | Positive |
| 2 | 1 | 2023-01-25 | Negative |
| 3 | 2 | 2023-02-01 | Positive |
| 4 | 2 | 2023-02-05 | Inconclusive |
| 5 | 2 | 2023-02-12 | Negative |
| 6 | 3 | 2023-01-20 | Negative |
| 7 | 3 | 2023-02-10 | Positive |
| 8 | 3 | 2023-02-20 | Negative |
| 9 | 4 | 2023-01-10 | Positive |
| 10 | 4 | 2023-01-18 | Positive |
| 11 | 5 | 2023-02-15 | Negative |
| 12 | 5 | 2023-02-20 | Negative |
+---------+------------+------------+--------------+
Output:
+------------+--------------+-----+---------------+
| patient_id | patient_name | age | recovery_time |
|------------|--------------|-----|---------------|
| 1 | Alice Smith | 28 | 10 |
| 3 | Carol Davis | 42 | 10 |
| 2 | Bob Johnson | 35 | 11 |
+------------+--------------+-----+---------------+
Explanation:
- Alice Smith (patient_id = 1):
- First positive test: 2023-01-15
- First negative test after positive: 2023-01-25
- Recovery time: 25 - 15 = 10 days
- Bob Johnson (patient_id = 2):
- First positive test: 2023-02-01
- Inconclusive test on 2023-02-05 (ignored for recovery calculation)
- First negative test after positive: 2023-02-12
- Recovery time: 12 - 1 = 11 days
- Carol Davis (patient_id = 3):
- Had negative test on 2023-01-20 (before positive test)
- First positive test: 2023-02-10
- First negative test after positive: 2023-02-20
- Recovery time: 20 - 10 = 10 days
- Patients not included:
- David Wilson (patient_id = 4): Only has positive tests, no negative test after positive
- Emma Brown (patient_id = 5): Only has negative tests, never tested positive
Output table is ordered by recovery_time in ascending order, and then by patient_name in ascending order.
Solution
# Write your MySQL query statement below
SELECT
p.patient_id,
p.patient_name,
p.age,
DATEDIFF(
min(neg.test_date),
min(pos.test_date)
) AS recovery_time
FROM
patients p
JOIN covid_tests pos ON
p.patient_id = pos.patient_id AND pos.result = 'Positive'
JOIN covid_tests neg ON
p.patient_id = neg.patient_id AND neg.result = 'Negative'
WHERE
neg.test_date > pos.test_date
GROUP BY
p.patient_id, p.patient_name, p.age
ORDER BY
recovery_time, p.patient_name;