MySQL Interview ,which made me disqualified for the job [closed] - mysql

Question

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.
Closed 10 years ago.
I was given this MySQL Interview Question, which made me disqualified for the job.
I went to interview and was asked a question which I was not able to reply and I lost the job.
They asked.
We have two tables, the first table (master table) is CANDIDATES with fields:
candidate_id (primary_key)
candidate_name
The Second table (child table) is CANDIDATE_VOTES with fields:
v_id (primary key)
candidate_id (foreign key)
Every time a vote is given the candidate's candidate_key is put in the child.
CANDIDATE:
=================================
|candidate_id | candidate_Name |
|-------------------------------|
| 1 | abc |
|-------------------------------|
| 2 | xyz |
|-------------------------------|
| 3 | etc |
|-------------------------------|
CANDIDATE VOTES
==========================
| votes_id | candidate_id |
|-------------------------|
| 1 | 1 |
|-------------------------|
| 2 | 1 |
|-------------------------|
| 3 | 2 |
|-------------------------|
The Question was how would you declare a winner?
Please help me how to do it.
I tried a lot but could not find the logic.

Answer 1

You should return all candidates who have the most number of votes:
SELECT candidates.*
FROM candidates JOIN candidate_votes USING (candidate_id)
GROUP BY candidate_id
HAVING COUNT(*) = (
SELECT COUNT(*)
FROM candidate_votes
GROUP BY candidate_id
ORDER BY votes DESC
LIMIT 1
)
See it on sqlfiddle.

Answer 2

You can use a COUNT() to get the total number of votes associated with each candidate. By joining the two tables, you can return the candidate_name and if you use a LIMIT and ORDER BY on the query it will return only the record determined as the winner.
SELECT count(*) winner, c.candidate_Name
FROM candidates c
INNER JOIN candidate_votes cv
ON c.candidate_id = cv.candidate_id
GROUP BY c.candidate_Name
ORDER BY winner desc
LIMIT 1 -- remove the LIMIT to see all records
See SQL Fiddle with Demo
or MySQL allows to GROUP BY on fields not in the SELECT
SELECT count(*) winner, , c.candidate_Name
FROM candidates c
INNER JOIN candidate_votes cv
ON c.candidate_id = cv.candidate_id
GROUP BY cv.candidate_id
ORDER BY winner desc
LIMIT 1 -- remove the LIMIT to see all records
See SQL Fiddle with Demo

Answer 3

SELECT CANDIDATE_NAME, count(*)
FROM CANDIDATES, CANDIDATE_VOTES
WHERE CANDIDATES.CANDIDATE_ID = CANDIDATE_VOTES.CANDIDATE_ID
GROUP BY CANDIDATE_NAME
ORDER BY count(*) DESC
LIMIT 1
SELECT: you select the candidate names + the amount of votes
FROM: use both tables
WHERE: basicly a join to link the tables
GROUP BY: Group the votes per candidate name, the count(*) in the SELECT will show you the amount of lines that were grouped into 1 line (a.k.a. the amount of votes per candidate)
ORDER BY: order by amount of votes highest to lowest
LIMIT: Will only return 1 row, remove this line to see complete list of candidates and votes

Answer 4

There are several ways to this. One would be to use a GROUP BY:
SELECT TOP 1 C.candidate_id, C.candidate_name, COUNT(1) NoOfVotes
FROM CANDIDATES C
INNER JOIN CANDIDATE_VOTES CV ON C.candidate_id = CV.candidate_id
GROUP BY C.candidate_id, , C.candidate_name
ORDER BY 3 DESC
This statement creates one row for each vote then groups these rows by candidate and counts how many rows are there for each candidate. Then it orders by the counted votes per candidate and selects the top 1 (doesn't deal with ties though).
Edit: This answer is valid for T-SQL (SQL Server). It seems from the other answers that you need to use "LIMIT 1" at the end instead of the "TOP 1" at the beginning for MySQL.