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.
#

# Write your MySQL query statement below

SELECT s.user_id,
  ROUND(IFNULL(SUM(c.action = 'confirmed') * 1.0 / COUNT(c.action), 0), 2) AS confirmation_rate
FROM Signups s
LEFT JOIN Confirmations c ON s.user_id = c.user_id
GROUP BY s.user_id;