Removing Last Comma within while loop - PHP - php

Question

I've been building a little tool to manage a dataset, I'm trying create a JSON output in order to serve my front-end the data.
Right now I have an extra comma at the end of every row in the loop. I need to remove it, it would be ideal if I can find a way to do this inside of the while loop.
Here is my code:
$sth = mysql_query("SELECT * FROM mapdata");
$num_rows = mysql_num_rows($sth);
$counter = 0;
echo '[';
while($r = mysql_fetch_assoc($sth)) {
if (++$counter == $num_rows) {
echo json_encode($r) . '';
}
else {
echo json_encode($r) . ',';
}
}
echo "]";
mysql_close($connection);
This is what I'm getting returned now
[
{"col1":"123","col2":"456","col3":"789",},
{"col1":"123","col2":"456","col3":"789",}
]
This is what I need.
[
{"col1":"data1","col2":"data2","col3":"data3"},
{"col1":"data1","col2":"data2","col3":"data3"}
]
Any suggestions would be greatly appreciated.

Answer 1

Your whole approach is wrong, you shouldn't try to create JSON by hand. Put all the rows in an array, and let json_encode() do it all for you.
$result = array();
while ($r = mysql_fetch_assoc($sth)) {
$result[] = $r;
}
echo json_encode($result);

Answer 2

I like to follow best practice whereever possible, but in this particular instance I needed to deviate from best practice due to some environment restrictions I had. I thought I'd share the solution I ended up using, regardless of it being overly complicated.
$sth = mysql_query("SELECT name,address,address2,city,state,postal,phone,lat,lng FROM mapdata");
$num_rows = mysql_num_rows($sth);
$counter = 0;
echo '[';
while($r = mysql_fetch_assoc($sth)) {
if (++$counter == $num_rows) {
echo preg_replace("/^,/",'',str_replace(',}','}',json_encode($r)));
}
else {
echo preg_replace("/^,/",'',str_replace(',}','}',json_encode($r)) . ',');
}
}
echo "]";
mysql_close($connection);