8/29 每日一題(MYSQL 輸出寵物分組, 排名比,評分低於3的機率)

Table: Queries

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| query_name  | varchar |
| result      | varchar |
| position    | int     |
| rating      | int     |
+-------------+---------+
There is no primary key for this table, it 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 an SQL query 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 query 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

# Write your MySQL query statement below

SELECT query_name,  ROUND(SUM(rating /position)/COUNT(query_name ) ,2 ) AS  quality ,

ROUND(AVG(rating <3)*100,2) AS poor_query_percentage

FROM Queries

GROUP BY query_name          

-------------------------

#依照寵物分組

#列出寵物名稱, 將rating/position 加總 再除寵物品種數 取小數後第二位

#計算rating不足3的平均

------------------------

# Write your MySQL query statement below

SELECT query_name,  ROUND(SUM(rating /position)/COUNT(query_name ) ,2 ) AS  quality ,

ROUND(SUM(rating <3)/COUNT(*) *100,2) AS poor_query_percentage

#SUM(條件式) 計算所有滿足條件的行數,這邊分組狗和貓各是1

#COUNT(*) 計算包含NULL的行數,所以是3, ps 只有COUNT(*)才會計算到NULL

FROM Queries

GROUP BY query_name          

-----------------參考解答

# Write your MySQL query statement below

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

-----------------

# Write your MySQL query statement below
SELECT query_name,

ROUND(SUM(rating/position)/(COUNT(query_name)),2) as quality, 

ROUND(AVG(IF(rating<3,1,0))*100,2) as poor_query_percentage 

FROM Queries 

GROUP BY query_name;