Add SQL solutions

* 1211
* 1633

Author: remy727

database/1211-queries-quality-and-percentage.sql

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+-- 1211. Queries Quality and Percentage
+-- Easy
+-- https://leetcode.com/problems/queries-quality-and-percentage
+
+/*
+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
+*/
+
+SELECT
+	query_name,
+	ROUND(AVG(1.0 * rating / position), 2) AS quality,
+	ROUND(100 * SUM(CASE WHEN rating < 3 THEN 1 ELSE 0 END)/ COUNT(*), 2) AS poor_query_percentage
+FROM
+	Queries
+GROUP BY
+	query_name;

database/1633-percentage-of-users-attended-a-contest.sql

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+-- 1633. Percentage of Users Attended a Contest
+-- Easy
+-- https://leetcode.com/problems/percentage-of-users-attended-a-contest
+
+/*
+Table: Users
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| user_id     | int     |
+| user_name   | varchar |
++-------------+---------+
+user_id is the primary key for this table.
+Each row of this table contains the name and the id of a user.
+
+Table: Register
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| contest_id  | int     |
+| user_id     | int     |
++-------------+---------+
+(contest_id, user_id) is the primary key for this table.
+Each row of this table contains the id of a user and the contest they registered into.
+
+Write an SQL query to find the percentage of the users registered in each contest rounded to two decimals.
+Return the result table ordered by percentage in descending order. In case of a tie, order it by contest_id in ascending order.
+The query result format is in the following example.
+
+Example 1:
+Input: 
+Users table:
++---------+-----------+
+| user_id | user_name |
++---------+-----------+
+| 6       | Alice     |
+| 2       | Bob       |
+| 7       | Alex      |
++---------+-----------+
+Register table:
++------------+---------+
+| contest_id | user_id |
++------------+---------+
+| 215        | 6       |
+| 209        | 2       |
+| 208        | 2       |
+| 210        | 6       |
+| 208        | 6       |
+| 209        | 7       |
+| 209        | 6       |
+| 215        | 7       |
+| 208        | 7       |
+| 210        | 2       |
+| 207        | 2       |
+| 210        | 7       |
++------------+---------+
+Output: 
++------------+------------+
+| contest_id | percentage |
++------------+------------+
+| 208        | 100.0      |
+| 209        | 100.0      |
+| 210        | 100.0      |
+| 215        | 66.67      |
+| 207        | 33.33      |
++------------+------------+
+Explanation: 
+All the users registered in contests 208, 209, and 210. The percentage is 100% and we sort them in the answer table by contest_id in ascending order.
+Alice and Alex registered in contest 215 and the percentage is ((2/3) * 100) = 66.67%
+Bob registered in contest 207 and the percentage is ((1/3) * 100) = 33.33%
+*/
+
+SELECT
+	contest_id,
+	ROUND(COUNT(user_id)*100.00/(SELECT COUNT(*) FROM Users), 2) as percentage
+FROM
+	Register
+GROUP BY
+	contest_id
+ORDER BY
+	percentage DESC,
+	contest_id;