Question

I’m currently working on a project of Voting System. I have a mysql database named “dbName” and
fields

`for table "pospresident"
---------------|-------------|---------------- \n
  idCandidate  |  NumOfVote  |  CandidateName  \n
---------------|-------------|---------------- \n
    1          |    20       |      Joe
    2          |    30       |      Carlo
---------------+-------------+----------------

for table "posvpres"

---------------|-------------|----------------
  idCandidate  |  NumOfVote  |  CandidateName 
---------------|-------------|----------------
    1          |    15       |      Anne
    2          |    35       |      Lucas
---------------+-------------+----------------

and so on ...

`

I just want to display all the names of candidate in different table who get the highest number of votes. I just need an idea on how my SELECT query should be.

Answer 1

Use UNION ALL to get the data from the two tables, then use GROUP BY with SUM and HAVING to get only this candidate that has the MAX votes. Something like this:

SELECT
  idCandidate,
  CandidateName,
  SUM(NumOfVote) Votes
FROM
(
    SELECT * 
    FROM  pospresident p
    UNION ALL
    SELECT * 
    FROM posvpres v 
) AS t
GROUP BY idCandidate, CandidateName
HAVING SUM(NumOfVote) = (SELECT MAX(NumOfVote) 
                         FROM
                         (
                             SELECT  NumOfVote FROM posvpres
                             UNION ALL
                             SELECT  NumOfVote FROM pospresident 
                         ) t);

SQL Fiddle Demo

This will give you:

| IDCANDIDATE | CANDIDATENAME | VOTES |
---------------------------------------
|           2 |         Lucas |    35 |