MySQL adding to query nullifies existing parts - php

Question

Database:
xx_users (id, name, user_id, email, location)
xx_questions (id, question, description, user_id)
Original code:
$friends = $facebook->api('/me/friends');
$arr= $friends['data'];
$friend_ids_arr = array();
foreach($arr as $friend) {
$friend_ids_arr[] = $friend['id'];
}
$sql = "SELECT * FROM xx_questions WHERE user_id IN (" . implode(',', $friend_ids_arr) . ") OR user_id = '$user' ORDER BY time DESC";
New code:
$friends = $facebook->api('/me/friends');
$arr= $friends['data'];
$friend_ids_arr = array();
foreach($arr as $friend) {
$friend_ids_arr[] = $friend['id'];
}
$sql = "SELECT *
FROM xx_questions q JOIN xx_users u ON
q.user_id = u.user_id
WHERE q.user_id IN (implode(',', $friend_ids_arr)) OR // STEP 1
q.user_id = '$user' OR // STEP 2
u.location = (SELECT location FROM xx_users WHERE user_id = $user) // STEP 3
ORDER BY q .time DESC";
$data = mysql_query($sql) or die(mysql_error());
while ($row = mysql_fetch_assoc($data)) {
echo $row[id];
}
I am trying to select questions from xx_questions (that have been posted by users) should any of three situations arise:
Those values where the poster's user_id matches that of one of the current user's friends (i.e. the poster and the user are friends)
Those values where the poster's user_id matches that of the user (i.e. the poster is the user)
Those values where the poster's location matches that of the current user (i.e. the poster and user are currently in the same city)
I had originally achieved steps 1 and 2, but when I add step 3, two things happen:
Step 1 stops working (i.e. only posts from the current user and people in the same city are returned)
The $row[id] echoed in the while loop is that of xx_users, not xx_questions. I've tried $row[q.id] but to no avail.
Any idea what's gone wrong?

Answer 1

In your seconds query your implode statement isnt outside the string.
"WHERE q.user_id IN (implode(',', $friend_ids_arr)) OR" // STEP 1
While php can add variable to a double quoted string ($x = "test $test test" $test will be changed to the value of $test) it can't escape functions. So this would return in
"WHERE q.user_id IN (implode(',', Array)) OR" // STEP 1
You should use:
"WHERE q.user_id IN (".implode(',', $friend_ids_arr).") OR" // STEP 1
And in the end you are using SELECT * and if both tables have an Id column, only one is returned. Its better to use SELECT q.* to get only the questions row or perhaps SELECT q.*, u.location to get the entire question row and the location from the user table.
I also checked your query and it should do what you want
$sql = "SELECT q.*, u.location
FROM xx_questions q
JOIN xx_users u
ON q.user_id = u.user_id
WHERE q.user_id IN (".implode(',', $friend_ids_arr).") OR // STEP 1
q.user_id = $user OR // STEP 2
u.location = (SELECT location FROM xx_users WHERE user_id = $user) // STEP 3
ORDER BY q.time DESC";
The only thing I changed is the implode and remove the '' around $user. That is incase the $user isnt actualy an integer but a string containing a number, but has some extra spaces appended (eg '1 ' instead of '1');