574. Winning Candidate

Description

Table: Candidate

+-------------+----------+
| Column Name | Type     |
+-------------+----------+
| id          | int      |
| name        | varchar  |
+-------------+----------+
id is the column with unique values for this table.
Each row of this table contains information about the id and the name of a candidate.

Table: Vote

+-------------+------+
| Column Name | Type |
+-------------+------+
| id          | int  |
| candidateId | int  |
+-------------+------+
id is an auto-increment primary key (column with unique values).
candidateId is a foreign key (reference column) to id from the Candidate table.
Each row of this table determines the candidate who got the ith vote in the elections.

Write a solution to report the name of the winning candidate (i.e., the candidate who got the largest number of votes).

The test cases are generated so that exactly one candidate wins the elections.

The result format is in the following example.

Example 1:

Input: 
Candidate table:
+----+------+
| id | name |
+----+------+
| 1  | A    |
| 2  | B    |
| 3  | C    |
| 4  | D    |
| 5  | E    |
+----+------+
Vote table:
+----+-------------+
| id | candidateId |
+----+-------------+
| 1  | 2           |
| 2  | 4           |
| 3  | 3           |
| 4  | 2           |
| 5  | 5           |
+----+-------------+
Output: 
+------+
| name |
+------+
| B    |
+------+
Explanation: 
Candidate B has 2 votes. Candidates C, D, and E have 1 vote each.
The winner is candidate B.

Solutions

Solution 1

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# Write your MySQL query statement below
SELECT
    Name
FROM
    (
        SELECT
            CandidateId AS id
        FROM Vote
        GROUP BY CandidateId
        ORDER BY COUNT(id) DESC
        LIMIT 1
    ) AS t
    INNER JOIN Candidate AS c ON t.id = c.id;

Solution 2

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# Write your MySQL query statement below
SELECT name
FROM
    Candidate AS c
    LEFT JOIN Vote AS v ON c.id = v.candidateId
GROUP BY c.id
ORDER BY COUNT(1) DESC
LIMIT 1;