Getting data from database showing it as json response - php

Question

In mysql table I have set of record. I want to fetch them wanna showlike below json response.
"results":[
{
"timestamp":"2014-03-04 17:26:14",
"id":"440736785698521089",
"category":"sports",
"username":"chetan_bhagat",
"displayname":"Chetan Bhagat"
}
I am getting above values i.e. timestamp,id,category,username from database. How can I show the result in form of json response like above?
UPDATE:
I fetch data in this way:
$con = mysqli_connect('127.0.0.1', 'root', '', 'mysql');
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
return;
}
$today = date("Ymd");
$result = mysqli_query($con,"SELECT url,img_url,sentiment,title,category from frrole_cateogry_article where category='".$category."' AND today <= '".$today."' AND title != '' AND img_url != '' order by url desc limit 3 ");
while ($row = #mysqli_fetch_array($result))
{
$url = $row['url'];
$img_url = $row['img_url'];
$screen_name = $row['screen_name'];
}

Answer 1

try this...
$con = mysqli_connect('127.0.0.1', 'root', '', 'mysql');
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
return;
}
$today = date("Ymd");
$result = mysqli_query($con,"SELECT url,img_url,sentiment,title,category from frrole_cateogry_article where category='".$category."' AND today <= '".$today."' AND title != '' AND img_url != '' order by url desc limit 3 ");
while ($row = #mysqli_fetch_array($result))
{
json_encode($row);
}

Answer 2

Fetch your results in the traditional way:
$data['results'] = $stmt->fetchAll(PDO::FETCH_ASSOC);
Then convert it all to JSON. Bam!
$results = json_encode($data);
This is far easier than trying to format JSON in your SQL query.
See for more details:
http://php.net/manual/en/pdostatement.fetchall.php
http://php.net/manual/en/function.json-encode.php
Since you're use mysqli instead of PDO, and using it in a procedural fashion, you'd fetch rows a different way:
while ($data['results'][] = mysql_fetch_assoc($result));
Then you can json_encode() as I showed above.