mysqli_fetch_assoc() is giving unexpected null values - php

Question

This is my SQL query:
SELECT * FROM users,content
LEFT OUTER JOIN articles ON (
content.content_id = articles.content_id
AND content.content_type = 'article' )
LEFT OUTER JOIN projects ON (
content.content_id = projects.content_id
AND content.content_type = 'project' )
LEFT OUTER JOIN videos ON (
content.content_id = articles.content_id
AND content.content_type = 'video' )
WHERE (content.content_id IN (128,414,399,616,259))
AND content.author_id = users.u_id
order by FIELD(content.content_id,128,414,399,616,259)
when I run this on phpmyadmin I'm getting the results correctly but when I fetch the results by doing mysqli_fetch_assoc(), I am getting null values for content_id. Someone please help me with this. Thanks in advance
Edit:
This is my php code
$query = "SELECT *
FROM users,content
LEFT OUTER JOIN articles
ON ( content.content_id = articles.content_id
AND content.content_type = 'article' )
LEFT OUTER JOIN projects
ON ( content.content_id = projects.content_id
AND content.content_type = 'project' )
LEFT OUTER JOIN videos
ON ( content.content_id = articles.content_id
AND content.content_type = 'video' )
WHERE (content.content_id IN (".implode(",",$new_array).")) AND content.author_id = users.u_id order by FIELD(content.content_id,".implode(",",$new_array).")";
$result = mysqli_query($con,$query);
if($result!=null && $result->num_rows>0){
while( $contentrow = $mysqli_fetch_assoc($result){
print_r($contentrow);
}
}
$new_array is the content ids for which I'm querying the database. The printed $contentrow has content_id field as null while I'm getting the correct id values in phpmyadmin.