Why does my PHP MYSQL Query not work with SUM? - php

Question

I don't get it.
This PHP - MYSQL query does work:
$sql = mysqli_prepare($conn, 'SELECT O.*
FROM OFFER O
LEFT JOIN EVENT E ON E.OFFER_ID = O.KEY_ID
LEFT JOIN BOOKING B ON B.EVENT_ID = E.KEY_ID
WHERE O.KEY_ID = ? ');
$sql->bind_param('i', $keyId);
With SUM statement it doesn't work:
$sql = mysqli_prepare($conn, 'SELECT O.*,
SUM(CASE WHEN B.KEY_ID IS NULL THEN 0 ELSE 1 END) AS BOOKING_COUNT
FROM OFFER O
LEFT JOIN EVENT E ON E.OFFER_ID = O.KEY_ID
LEFT JOIN BOOKING B ON B.EVENT_ID = E.KEY_ID
WHERE O.KEY_ID = ? ');
$sql->bind_param('i', $keyId);
Error message:
Uncaught Error: Call to a member function bind_param() on boolean in ..snippet-ops.php(361) : eval()'d code:107
The query works in phpmyadmin though.Does anyone know why?
EDIT: SOLVED: The accepted Answer contains the solution in the comments (turning on report and a GROUP BY solved the issue.
EDIT2: When downgrading a question it would be good to know why otherwise the downgrade is useless.

Answer 1

Try surrounding your query string with double quotes instead of single quotes. Beware, that prepare might return false instead of a statement object. You should check this and react accordingly. Also make sure to close your statement after you're done with it.
Here (not tested):
<?php
$sql = "
SELECT O.*, SUM(CASE WHEN B.KEY_ID IS NULL THEN 0 ELSE 1 END) AS BOOKING_COUNT
FROM OFFER O
LEFT JOIN EVENT E ON E.OFFER_ID = O.KEY_ID
LEFT JOIN BOOKING B ON B.EVENT_ID = E.KEY_ID
WHERE O.KEY_ID = ?
GROUP BY O.KEY_ID";
if ($stmt = $conn->prepare($sql)) {
$stmt->bind_param("i", $keyId);
$stmt->execute();
// do stuff with $stmt
$stmt->close();
} else {
echo $stmt->error;
}
?>
UPDATE: As can be seen in the comments, it was necessary to group by the column O.KEY_ID, or the prepare would return false.