MySQL Count不填充变量

Question

Problem is: I want to count the number in my column r_start where the r_start dates are between my other two variables. But it always gives me the Error Notice: Undefined variable: z in [path] on line 173. So it doesn't fill the variable, what makes me think that the COUNT does not work porperly. I did a lot of reasearch and tried some things, but I simply don't find the cause..

$sqld = "SELECT r_start, COUNT (*) FROM reservation WHERE r_start BETWEEN '".$cid."' and '".$cod."' GROUP BY r_start";
if ($result = $con->query($sqld)) {
    $z = mysqli_fetch_assoc($result);
}

This error only appears with the COUNT tag. In my other queries it works absolutly fine. f.e.:

$sqlc = "SELECT * FROM reservation where r_ende between '".$cid."' and '".$cod."'";
if ($result = $con->query($sqlc)) {
    $y = mysqli_fetch_assoc($result);
}

Can anybody tell my why? Have I done something wrong?

Answer 1

MySQL generally does not recognize a space between a function and the opening paren. I would also advise that you give the column an alias:

SELECT r_start, COUNT(*) as cnt
FROM reservation r
WHERE r_start BETWEEN '".$cid."' and '".$cod."'
GROUP BY r_start;

You should also learn to use parameters to pass values into queries. Not using parameters makes the code subject to unexpected (and hard-to-debug) syntax errors, as well as making it vulnerable to SQL injection.