task: #3586

README.md

@@ -190,6 +190,7 @@ Useful for preparing for technical interviews and improving your SQL skills.
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     - [3564. Seasonal Sales Analysis](./leetcode/medium/3564.%20Seasonal%20Sales%20Analysis.sql)
     - [3580. Find Consistently Improving Employees](./leetcode/medium/3580.%20Find%20Consistently%20Improving%20Employees.sql)
+    - [3586. Find COVID Recovery Patients](./leetcode/medium/3586.%20Find%20COVID%20Recovery%20Patients.sql)
     - [3601. Find Drivers with Improved Fuel Efficiency](./leetcode/medium/3601.%20Find%20Drivers%20with%20Improved%20Fuel%20Efficiency.sql)
 3. [Hard](./leetcode/hard/)
     - [185. Department Top Three Salaries](./leetcode/hard/185.%20Department%20Top%20Three%20Salaries.sql)

leetcode/medium/3586. Find COVID Recovery Patients.sql

@@ -0,0 +1,67 @@
+/*
+Question 3586. Find COVID Recovery Patients
+Link: https://leetcode.com/problems/find-covid-recovery-patients/description/?envType=problem-list-v2&envId=database
+
+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.
+*/
+
+WITH first_positive AS (
+    SELECT
+        patient_id,
+        MIN(test_date) AS positive
+    FROM covid_tests
+    WHERE result = 'Positive'
+    GROUP BY patient_id
+),
+
+first_negative AS (
+    SELECT
+        ct.patient_id,
+        MIN(ct.test_date) AS negative,
+        MIN(fp.positive) AS positive
+    FROM covid_tests AS ct
+    LEFT JOIN 
+        first_positive AS fp
+        ON ct.patient_id = fp.patient_id
+    WHERE ct.result = 'Negative' AND ct.test_date > fp.positive
+    GROUP BY ct.patient_id
+)
+
+SELECT
+    fn.patient_id,
+    p.patient_name,
+    p.age,
+    fn.negative - fn.positive AS recovery_time
+FROM first_negative AS fn
+LEFT JOIN
+    patients AS p
+    ON fn.patient_id = p.patient_id
+ORDER BY recovery_time ASC, p.patient_name ASC