Another reason why an undefined index notice will be thrown, would be that a column was omitted from a database query.
I.e.:
$query = "SELECT col1 FROM table WHERE col_x = ?";
Then trying to access more columns/rows inside a loop.
I.e.:
print_r($row['col1']);
print_r($row['col2']); // undefined index thrown
or in a while
loop:
while( $row = fetching_function($query) ) {
echo $row['col1'];
echo "<br>";
echo $row['col2']; // undefined index thrown
echo "<br>";
echo $row['col3']; // undefined index thrown
}
Something else that needs to be noted is that on a *NIX OS and Mac OS X, things are case-sensitive.
Consult the followning Q&A's on Stack: