Table: Ads
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| ad_id | int |
| user_id | int |
| action | enum |
+---------------+---------+
(ad_id, user_id) is the primary key for this table.
Each row of this table contains the ID of an Ad, the ID of a user, and the action taken by this user regarding this Ad.
The action column is an ENUM type of ('Clicked', 'Viewed', 'Ignored').
A company is running Ads and wants to calculate the performance of each Ad.
Performance of the Ad is measured using Click-Through Rate (CTR) where:
Write an SQL query to find the ctr of each Ad. Round ctr to two decimal points.
Return the result table ordered by ctr in descending order and by ad_id in ascending order in case of a tie.
The query result format is in the following example.
Example 1:
Input: Ads table: +-------+---------+---------+ | ad_id | user_id | action | +-------+---------+---------+ | 1 | 1 | Clicked | | 2 | 2 | Clicked | | 3 | 3 | Viewed | | 5 | 5 | Ignored | | 1 | 7 | Ignored | | 2 | 7 | Viewed | | 3 | 5 | Clicked | | 1 | 4 | Viewed | | 2 | 11 | Viewed | | 1 | 2 | Clicked | +-------+---------+---------+ Output: +-------+-------+ | ad_id | ctr | +-------+-------+ | 1 | 66.67 | | 3 | 50.00 | | 2 | 33.33 | | 5 | 0.00 | +-------+-------+ Explanation: for ad_id = 1, ctr = (2/(2+1)) * 100 = 66.67 for ad_id = 2, ctr = (1/(1+2)) * 100 = 33.33 for ad_id = 3, ctr = (1/(1+1)) * 100 = 50.00 for ad_id = 5, ctr = 0.00, Note that ad_id = 5 has no clicks or views. Note that we do not care about Ignored Ads.
SELECT
ad_id,
Ifnull(ROUND(AVG(CASE
WHEN action = 'Clicked' THEN 1
WHEN action = 'Viewed' THEN 0
ELSE NULL
END) * 100, 2), 0) AS ctr
FROM ads
GROUP BY ad_id
ORDER BY ctr DESC,
ad_id ASC;