Avoid null results from query - php

Question

suppose this
user table:
[id] [mail] [pass]
happen table:
[id] [uid] [date] [content]
vote table
[uid] [hid] [type] [datetime]
1 user can have 0 or more happen, 1 happen can have 0 or more votes..
I want to get the total number of votes for a specific happen
SELECT
H.*,
SUM(CASE WHEN V.type='C' THEN 1 ELSE 0 END) AS upvotes,
SUM(CASE WHEN V.type='R' THEN 1 ELSE 0 END) AS downvotes
FROM
happens H
LEFT JOIN
votes AS V
ON V.hid = H.id
WHERE
H.uid = :uid
the problem is that if no votes is associated on a happen I get a null row from mysql, not EMPTY but NULL
how can I avoid this null result?
[edit]
some try:
basic
SELECT H.* FROM happens H LEFT JOIN votes AS V ON V.hid = H.id WHERE H.uid = '178d937'
result -> empty
All other try with the SUM, COUNT, HAVING ect ect gives:
[id] [uid] [what] [latitude] [longitude] [date] [time] [hide] [upvotes] [downvotes]
NULL NULL NULL NULL NULL NULL NULL NULL 0 0

Answer 1

Use HAVING to check for the null
SELECT
H.*,
SUM(CASE WHEN V.type='C' THEN 1 ELSE 0 END) AS upvotes,
SUM(CASE WHEN V.type='R' THEN 1 ELSE 0 END) AS downvotes
FROM
happens H
LEFT JOIN
votes AS V
ON V.hid = H.id
WHERE
H.uid = :uid
HAVING upvotes IS NOT NULL

Answer 2

SELECT H.*,
SUM(IFNULL(V.type = 'C', 0)) AS upvotes,
SUM(IFNULL(V.type = 'R', 0)) AS downvotes

Answer 3

If you change your LEFT JOIN to an INNER JOIN (or just JOIN) you will only get the happens records that have at least 1 associated record in the votes table:
SELECT
H.*,
SUM(CASE WHEN V.type='C' THEN 1 ELSE 0 END) AS upvotes,
SUM(CASE WHEN V.type='R' THEN 1 ELSE 0 END) AS downvotes
FROM
happens H
INNER JOIN
votes AS V
ON V.hid = H.id
WHERE
H.uid = :uid
Check out http://www.w3schools.com/sql/sql_join.asp for info on the different join types.
EDIT:
Ok, so to get all happens, but with 0 for those without votes try (add COALESCE):
SELECT
H.*,
COALESCE(SUM(CASE WHEN V.type='C' THEN 1 ELSE 0 END),0) AS upvotes,
COALESCE(SUM(CASE WHEN V.type='R' THEN 1 ELSE 0 END),0) AS downvotes
FROM
happens H
LEFT JOIN
votes AS V
ON V.hid = H.id
WHERE
H.uid = :uid

Answer 4

SELECT
H.*,
COALESCE(SUM(CASE WHEN V.type='C' THEN 1 ELSE 0 END), 0) AS upvotes,
COALESCE(SUM(CASE WHEN V.type='R' THEN 1 ELSE 0 END), 0) AS downvotes

Answer 5

Left Join will return all rows on the left and NULL values on the right if ON condition does not match.Use Inner Join.

Answer 6

solved using 2 statement
first select all happen
second select all votes for every happen and merging the values
here is the solution from my php happenModel class:
public function getUserHappensWithVotes() {
$selectQuery = <<<QUERY
SELECT
SUM(CASE WHEN V.type='C' THEN 1 ELSE 0 END) AS upvotes,
SUM(CASE WHEN V.type='R' THEN 1 ELSE 0 END) AS downvotes
FROM
votes V
WHERE
V.uid = :uid
AND
V.hid = :hid
QUERY;
// get all happen as array of class
$userHappens = $this->userHappens;
// empty container
$happenWithVotes = array();
foreach( $userHappens AS $happen ) {
$sql = $this->pdo->prepare( $selectQuery );
$sql->execute( array( ':uid'=>$happen->uid, ':hid'=>$happen->id ) );
// fetching the count of up and down votes of every happen
$votes = $sql->fetch( PDO::FETCH_ASSOC );
// merging happen class as array with votes
$happen = array_merge( (array) $happen, $votes );
// rebuild the userHappen array
$happenWithVotes[] = (object) $happen;
}
if ( $this->encoder ) {
return $this->encoder->setData( $this->parse( $happenWithVotes ) )->encode();
} else {
return $this->parse( $happenWithVotes );
}
}