LeetCode 1934.sql

-- Question: 1934. Confirmation Rate.

--   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.

-- The result format is in the following example.

 

-- Example 1:

-- Input: 
-- Signups table:
-- +---------+---------------------+
-- | user_id | time_stamp          |
-- +---------+---------------------+
-- | 3       | 2020-03-21 10:16:13 |
-- | 7       | 2020-01-04 13:57:59 |
-- | 2       | 2020-07-29 23:09:44 |
-- | 6       | 2020-12-09 10:39:37 |
-- +---------+---------------------+
-- Confirmations table:
-- +---------+---------------------+-----------+
-- | user_id | time_stamp          | action    |
-- +---------+---------------------+-----------+
-- | 3       | 2021-01-06 03:30:46 | timeout   |
-- | 3       | 2021-07-14 14:00:00 | timeout   |
-- | 7       | 2021-06-12 11:57:29 | confirmed |
-- | 7       | 2021-06-13 12:58:28 | confirmed |
-- | 7       | 2021-06-14 13:59:27 | confirmed |
-- | 2       | 2021-01-22 00:00:00 | confirmed |
-- | 2       | 2021-02-28 23:59:59 | timeout   |
-- +---------+---------------------+-----------+
-- Output: 
-- +---------+-------------------+
-- | user_id | confirmation_rate |
-- +---------+-------------------+
-- | 6       | 0.00              |
-- | 3       | 0.00              |
-- | 7       | 1.00              |
-- | 2       | 0.50              |
-- +---------+-------------------+
-- Explanation: 
-- User 6 did not request any confirmation messages. The confirmation rate is 0.
-- User 3 made 2 requests and both timed out. The confirmation rate is 0.
-- User 7 made 3 requests and all were confirmed. The confirmation rate is 1.
-- User 2 made 2 requests where one was confirmed and the other timed out. The confirmation rate is 1 / 2 = 0.5.


Query:
    select t.user_id,coalesce(round((select count(*) from Confirmations c 
    where action='confirmed' and t.user_id=c.user_id)/(select count(*) 
    from Confirmations c where t.user_id=c.user_id),2),0.00) as confirmation_rate from Signups t;