Syntax Error for around LIMIT - mysql

Question

I'm working on a training course for PHP and I think the mysql syntax is outdated. This is the function
function get_subject_by_id($subject_id) {
global $connection;
$query = "SELECT * ";
$query .= "FROM subjects ";
$query .= "WHERE id=" . $subject_id ." ";
$query .= "LIMIT 1";
$result_set = mysql_query($query, $connection);
confirm_query($result_set);
if ($subject = mysql_fetch_array($result_set)) {
return $subject;
} else {
return NULL;
}
}
and I'm getting back this error:
Database query failed: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'LIMIT 1' at line 1
I'm not sure what I'm doing wrong here. Any help from someone who knows what might have changed in the syntax would be greatly appreciated.

Answer 1

$query = "SELECT *
FROM subjects
WHERE id = $subject_id
LIMIT 1";
Query fails because $subject_id is empty.
SELECT * FROM subjects WHERE id= LIMIT 1

Answer 2

apparently the $subject_id is causing the trouble, check if the value is passed correctly.

Answer 3

Two wild guesses:
You did not quote / escape $subject_id which contains a string or something non-integer (such as FALSE, NULL or the empty string).
Even if this is not the cause, it makes your script vulnerable to SQL injection.
You are using a Mac for coding and have erroneously inserted a non-breakable space