mysqli_multi_query array issue - php

Question

There's something weird going on.
I have I database which could look something like this:
table name: dm
|id|receiver|sender|msg |
|1 |John |Emma |Hey John! |
|2 |Emma |John |Hey! |
|3 |John |Emma |Whats up |
|4 |Emma |John |Not too much |
|5 |John |Keira |Have you got...|
I have an html page with a on it and for now what I want is for the messages that either
Emma sent to John => receiver = "John", sender = "Emma" or
John sent to Emma => receiver = "Emma", sender = "John"
to be displayed in the console.
I can do that with JQuery using the console.log() function.
My PHP looks like this:
$user1 = "John";
$user2 = "Emma";
$sql = "SELECT * FROM dm WHERE receiver = '$user1' AND sender = '$user2';SELECT * FROM dm WHERE receiver = '$user2' AND sender = '$user1'";
// Execute multi query
if (mysqli_multi_query($link,$sql))
{
do
{
$i = 0;
$msg = array();
if ($result=mysqli_store_result($link)) {
while ($row=mysqli_fetch_row($result))
{
printf("%s\n",$row[0]);
$msg[$i] = $row[0];
$i++;
}
mysqli_free_result($result);
}
}
while (mysqli_next_result($link));
}
echo json_encode($msg);
exit();
mysqli_close($link);
You will notice, that I have "printf" in there, because I wanted to see what the databse would give back to me. It correctly gave back the id's: 1,3,2,4.
However, I normally would like to do the request using JQuery ajax. I know how to do that also. Because of that I want to have an array which holds all the id's of the posts like this:
["1","2","3","4"]
Unfortunately the way I do it as written in the code what it returns to me is this:
["2","4"]
So what's going on is that he only puts what was in the first query into the array.
So what exactly is my question?
I want to fix the array to hold all the id's of the respective messages which would be 1,2,3,4. Preferably in this order as well and not like this 1,3,2,4.
I hope I made the problem clear and thank you for any advice!

Answer 1

You reset $i and $msg inside the outer loop. That means you will only see results from the second query in your array. Move the $i = 0; and $msg = array(); lines outside that loop.
That said, there’s no reason to do 2 queries here. Just use an OR in your WHERE clause to get both results at once. This will be faster and easier.
Also, this is very important: you are wide open to SQL injection. You need to use prepared statements, rather than concatenating variables into your query. See How can I prevent SQL injection in PHP?.