Winning Candidate - Practice Coding Problems

Winning Candidate - Problem

Database Medium

You are given two tables representing an election system:

Table: Candidate

id (int): Unique identifier for each candidate
name (varchar): Name of the candidate

Table: Vote

id (int): Auto-increment primary key for each vote
candidateId (int): Foreign key referencing the candidate who received this vote

Write a SQL query to find the name of the winning candidate - the candidate who received the most votes. The test cases guarantee that exactly one candidate wins the election.

Table Schema

Candidate

Column Name	Type	Description
`id` PK	int	Unique identifier for each candidate
`name`	varchar	Name of the candidate

Primary Key: id

Vote

Column Name	Type	Description
`id` PK	int	Auto-increment primary key for each vote
`candidateId`	int	Foreign key referencing the candidate who received this vote

Primary Key: id

Input & Output

Example 1 — Basic Election

Input Tables:

Candidate

id	name
2	Bob
3	Alice
4	Carol

Vote

id	candidateId
1	2
2	4
3	3
4	2
5	2

Output:

name
Bob

💡 Note:

Bob received 3 votes (vote IDs 1, 4, 5), Alice received 1 vote (vote ID 3), and Carol received 1 vote (vote ID 2). Bob has the most votes, so he wins the election.

Example 2 — Close Election

Input Tables:

Candidate

id	name
1	John
2	Jane

Vote

id	candidateId
1	1
2	2
3	1
4	1

Output:

name
John

💡 Note:

John received 3 votes (vote IDs 1, 3, 4) and Jane received 1 vote (vote ID 2). John wins with the majority of votes.

Constraints

1 ≤ candidate.id ≤ 100
1 ≤ vote.candidateId ≤ 100
1 ≤ total votes ≤ 1000
Exactly one candidate wins the election

Visualization

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Understanding the Visualization

Join Tables

Connect Vote and Candidate tables

Group & Count

GROUP BY candidate and COUNT votes

Find Winner

ORDER BY count DESC, LIMIT 1

Key Takeaway

🎯 Key Insight: Use GROUP BY with COUNT to aggregate votes, then JOIN to get readable results

Asked in

a Amazon 28 M Microsoft 22 f Facebook 18 G Google 15

Use GROUP BY to count votes per candidate, JOIN with Candidate table to get names, then ORDER BY vote count descending and LIMIT 1 to find the winner.

Table Schema

Candidate

Column Name	Type	Description
`id` PK	int	Unique identifier for each candidate
`name`	varchar	Name of the candidate

Primary Key: id

Vote

Column Name	Type	Description
`id` PK	int	Auto-increment primary key for each vote
`candidateId`	int	Foreign key referencing the candidate who received this vote

Primary Key: id

Common Approaches

Approach	Time	Space	Notes
✓ GROUP BY with COUNT and JOIN	O(n + m)	O(m)	Count votes per candidate using GROUP BY, then join with Candidate table to get the winner's name

GROUP BY with COUNT and JOIN — Algorithm Steps

Step 1: Count votes for each candidate using GROUP BY candidateId
Step 2: JOIN with Candidate table to get candidate names
Step 3: ORDER BY vote count descending and LIMIT 1 to get the winner

Visualization

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Step-by-Step Walkthrough

Group Votes

Group by candidateId

Count

COUNT(*) votes per group

Join & Order

Join with Candidate table and order by count

Code -

solution.c — C

Time & Space Complexity

Time Complexity

⏱️

O(n + m)

n votes to count + m candidates to join

✓ Linear Growth

Space Complexity

O(m)

Space for grouped results per candidate

✓ Linear Space

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Smart Actions

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Table Schema

Input & Output

Constraints

Visualization

Related Problems

Table Schema

Common Approaches

GROUP BY with COUNT and JOIN — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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