Concatenation with addition in it doesn't work as expected

Solution 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.

Solution 2:

This is happening because of the operator precedence. Try with -

$sql .= '(' 
           . ((int)$data['event_id']) . ', ' 
           . ($key + 1) . ', ' 
           . ((int)$val['file_id']) . ', "' 
           . addslashes($val['url']) . 
         '"), ';