task: #1934

Author: Ivanbyone

README.md

@@ -81,6 +81,7 @@ Have a good contributing!
     - [1193. Monthly Transactions I](./leetcode/medium/1193.%20Monthly%20Transactions%20I.sql)
     - [1341. Movie Rating](./leetcode/medium/1341.%20Movie%20Rating.sql)
     - [1907. Count Salary Categories](./leetcode/medium/1907.%20Count%20Salary%20Categories.sql)
+    - [1934. Confirmation Rate](./leetcode/medium/1934.%20Confirmation%20Rate.sql)
 3. [Hard](./leetcode/hard/)
     - [185. Department Top Three Salaries](./leetcode/hard/185.%20Department%20Top%20Three%20Salaries.sql)
 

leetcode/medium/1934. Confirmation Rate.sql

@@ -0,0 +1,54 @@
+/*
+Question 1934. Confirmation Rate
+Link: https://leetcode.com/problems/confirmation-rate/description/?envType=study-plan-v2&envId=top-sql-50
+
+Table: Signups
+
++----------------+----------+
+| Column Name    | Type     |
++----------------+----------+
+| user_id        | int      |
+| time_stamp     | datetime |
++----------------+----------+
+user_id is the column of unique values for this table.
+Each row contains information about the signup time for the user with ID user_id.
+ 
+
+Table: Confirmations
+
++----------------+----------+
+| Column Name    | Type     |
++----------------+----------+
+| user_id        | int      |
+| time_stamp     | datetime |
+| action         | ENUM     |
++----------------+----------+
+(user_id, time_stamp) is the primary key (combination of columns with unique values) for this table.
+user_id is a foreign key (reference column) to the Signups table.
+action is an ENUM (category) of the type ('confirmed', 'timeout')
+Each row of this table indicates that the user with ID user_id requested a confirmation message at time_stamp and that confirmation message was either confirmed ('confirmed') or expired without confirming ('timeout').
+ 
+
+The confirmation rate of a user is the number of 'confirmed' messages divided by the total number of requested confirmation messages. The confirmation rate of a user that did not request any confirmation messages is 0. Round the confirmation rate to two decimal places.
+
+Write a solution to find the confirmation rate of each user.
+
+Return the result table in any order.
+*/
+
+SELECT
+    s.user_id,
+    COALESCE(CASE
+        WHEN c.user_id IS NULL THEN 0.00
+        ELSE ROUND((
+            SELECT COUNT(c2.user_id)
+            FROM Confirmations AS c2
+            WHERE c2.action = 'confirmed' AND c2.user_id = s.user_id
+            GROUP BY c2.user_id
+        ) / COUNT(c.user_id)::numeric, 2)
+    END, 0.00) AS confirmation_rate
+FROM Signups AS s
+LEFT JOIN 
+    Confirmations AS c
+    ON s.user_id = c.user_id
+GROUP BY s.user_id, c.user_id