Joining two tables based off a condition SQL - php

Question

I am building an android app that uses geo location. I am trying to improve my overall app to improve its smoothness while running. I am using volly to connect to a php page on my web sever where the php page can then access my phpmyadmin database. My php page for updating locations is a horrible mess and I was hoping it can be fixed with the right sql query.
Lets get down to it.
So I have a table named users
and a table named friends
In this particular example david is friends with mark and jack. Also to clarify mark and jack are friends with david.
What I need to do is Write a query if given a user ID say for example 3 that will produce a table of that person and his friends ID, cordsV1, cordsV2 without any duplicate IDs in the table.
I was able to get this to work with using loops and variables ect but as I said it is a horrible mess.
Here is my current all sql query attempt:
SELECT DISTINCT ID, cordsV1, cordsV2 FROM `friends`,`users` WHERE user_one_ID = 1 AND status = 1;
HOWEVER this just returns all of the user IDs from the user table. I am really bad with sql so if someone could point me in the right direction it would be much appreciated.
Here is my horrible mess of code if you were wondering:
<?php error_reporting(E_ALL | E_STRICT); ?>
<?php
$THIS_USER_ID = $_GET['THIS_USER_ID'];
try {
$one = 1;
$db = new PDO("");
$sql = "SELECT * FROM friends WHERE user_one_ID = '" . $THIS_USER_ID . "' AND status = '" . $one . "' OR user_two_ID = '" . $THIS_USER_ID . "' AND status = '" . $one . "'";
$rows = $db->query($sql)
->fetchAll(PDO::FETCH_ASSOC);
$printMe = [];
foreach($rows as $row){
$printMe[] = $row;
}
$jsonArr = json_encode($printMe);
$characters = json_decode($jsonArr, true);
// Getting the size of the sample array
$size = sizeof($characters);
$neg = -1;
$sql2 = "SELECT * FROM users WHERE ID = '" . $neg . "'";
$sql3 = "";
$sql4 = "";
for ($x = 0; $x < $size; $x++ ){
if ($characters[$x]['user_one_ID'] == $THIS_USER_ID && $characters[$x]['status'] == 1){
$hold = $characters[$x]['user_two_ID'];
$sql3 = $sql3 . " OR ID = '" . $hold . "'";
} else if($characters[$x]['user_two_ID'] == $THIS_USER_ID && $characters[$x]['status'] == 1) {
$hold = $characters[$x]['user_one_ID'];
$sql4 = $sql4 . " OR ID = '" . $hold . "'";
}
}
$sql5 = $sql2 . $sql3 . $sql4;
$sql7 = "SELECT * FROM users WHERE ID = '" . $THIS_USER_ID . "'";
$printMe2 = [];
$rows3 = $db->query($sql7)
->fetchAll(PDO::FETCH_ASSOC);
foreach($rows3 as $row3){
$printMe2[] = $row3;
}
$rows2 = $db->query($sql5)
->fetchAll(PDO::FETCH_ASSOC);
foreach($rows2 as $row2){
$printMe2[] = $row2;
}
$jsonArr2 = json_encode($printMe2);
echo $jsonArr2;
$db = null;
} catch(PDOException $ex) {
die(json_encode(array('outcome' => false, 'message' => 'Unable to connect')));
}
?>

Answer 1

Get the user-data
SELECT
*
FROM
users
WHERE ID = ?
Get the user-data of friends
SELECT
users.*
FROM
friends
JOIN
users ON users.ID = friends.user_two_ID
WHERE
friends.user_one_ID = ?
Better use prepared statements, or your app wont be alive very long due to SQL-Injections.
You also want to have a look at meaningful names.