Why only some mysqli queries work? - php

Question

I am facing a problem with mysqli select queries.
The table I am using is called participant and has the following fields:
id int(11) AI PK
name varchar(255)
surname varchar(255)
birth varchar(32)
sex varchar(32)
email varchar(255)
telephone varchar(32)
club varchar(255)
startingGroup int(2)
This is a PHP file (called select.php):
$connection = mysqli_connect("localhost", "$user", "$pass", "$db_name");
$query = "SELECT id, name, surname FROM participant WHERE NOT 0";
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
if (!mysqli_query($connection, $query)) {
printf("Errormessage: %s\n", mysqli_error($connection));
}
$result = mysqli_query($connection, $query);
$arr = array();
if(mysqli_num_rows($result) != 0) {
while($row = mysqli_fetch_assoc($result)) {
$arr[] = $row;
}
}
mysqli_close($connection);
echo $json_info = json_encode($arr);
which is later called by AngularJS in:
$http.post("select.php").success(function(data){
console.log(data);
$scope.newparticipants = jsonFilter(data);
console.log($scope.newparticipants);
});
The value returned by the first console.log is 'undefined' and by the second "". When I change my query to select only 'id' the whole thing works and data is visible. Any guess why it is so?

Answer 1

It occurred that in the database there were some diacritical marks coded in utf8_general_ci. I didn't have a clue on what's going on, because some queries responded correctly, some not. Selecting ids from particular range I was receiving a correct result. Selecting a range beside - I was getting undefined. I found it very hard to detect that the problem was with encoding(only some rows contained these diacritical marks).
If you are in a similar situation - check if your database has some non-standard encoding. If so define it in your code, just after opening a database connection, for example:
(procedural style)
mysqli_set_charset($connection,"utf8");
(object-oriented)
$mysqli->set_charset("utf8")
Thank you all for trying to resolve this problem.