SQL | LeetCode 1211. Query 품질과 Poor Query 비율 계산하기

SELECT 
    query_name, 
    ROUND(AVG(rating / position), 2) AS quality,
    ROUND(SUM(rating < 3) / COUNT(*) * 100, 2) AS poor_query_percentage 
FROM queries
GROUP BY query_name;

Table: Queries

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| query_name  | varchar |
| result      | varchar |
| position    | int     |
| rating      | int     |
+-------------+---------+
This table may have duplicate rows.
This table contains information collected from some queries on a database.
The position column has a value from 1 to 500.
The rating column has a value from 1 to 5. Query with rating less than 3 is a poor query.

 

We define query quality as:

The average of the ratio between query rating and its position.

We also define poor query percentage as:

The percentage of all queries with rating less than 3.

Write a solution to find each query_name, the quality and poor_query_percentage.

Both quality and poor_query_percentage should be rounded to 2 decimal places.

Return the result table in any order.

The result format is in the following example.

 

Example 1:

Input: 
Queries table:
+------------+-------------------+----------+--------+
| query_name | result            | position | rating |
+------------+-------------------+----------+--------+
| Dog        | Golden Retriever  | 1        | 5      |
| Dog        | German Shepherd   | 2        | 5      |
| Dog        | Mule              | 200      | 1      |
| Cat        | Shirazi           | 5        | 2      |
| Cat        | Siamese           | 3        | 3      |
| Cat        | Sphynx            | 7        | 4      |
+------------+-------------------+----------+--------+
Output: 
+------------+---------+-----------------------+
| query_name | quality | poor_query_percentage |
+------------+---------+-----------------------+
| Dog        | 2.50    | 33.33                 |
| Cat        | 0.66    | 33.33                 |
+------------+---------+-----------------------+
Explanation: 
Dog queries quality is ((5 / 1) + (5 / 2) + (1 / 200)) / 3 = 2.50
Dog queries poor_ query_percentage is (1 / 3) * 100 = 33.33

Cat queries quality equals ((2 / 5) + (3 / 3) + (4 / 7)) / 3 = 0.66
Cat queries poor_ query_percentage is (1 / 3) * 100 = 33.33

각 query_name에 대해 다음 두 가지 값을 구하는 SQL 쿼리를 작성하는 문제입니다.

1. query quality: (rating / position) 값들의 평균 (소수 둘째 자리까지 반올림)
2. poor_query_percentage: rating < 3인 쿼리 비율 (소수 둘째 자리까지 반올림)

select 
    query_name, 
    round(avg(rating/position),2) as quality,
    round(sum(rating < 3)/count(*) * 100,2) as poor_query_percentage 
from queries
group by query_name

AVG(rating / position)는 각 행에서 rating / position을 먼저 계산한 후 평균을 구합니다. 조건문을 그대로 SUM()에 넣어주면 불리언 값이 1(true), 0(false)로 처리됩니다. 즉, rating이 3보다 작은 경우만 합쳐지므로 poor query의 개수를 셉니다.