php - Concatenation with addition in it doesn't work as expected

Question

Here is my PHP code with SQL query, but the output isn't as expected:

$sql = 'INSERT INTO `event_footers` (`event_id`, `order`, `file_id`, `url`) VALUES ';
foreach($all_footers as $key => $val){
    $sql .= '('.(int)$data['event_id'].', '.$key + 1 .', '.(int)$val['file_id'].', "'.addslashes($val['url']).'"), ';
}

$sql = rtrim($sql, ', ');
var_dump($sql);
exit;

AND I get sql query like this:

`INSERT INTO `event_footers` (`event_id`, `order`, `file_id`, `url`) VALUES 1, 2135, "http://11.lt"), 1, 2136, "http://22.lt"), 1, 2140, "http://44.lt")`

Where is the first ( after VALUES?

Answer 1

+ and . have the same operator precedence, but are left associative. Means after the first concatenation:

'(' . (int)$data['event_id']

The string got added with your key, e.g.

"($data['event_id']" + $key

So the string gets converted into an integer in that numerical context and disappears. To solve this use parentheses () around your addition.