Difference between PHP Arrays and possible output

问题

Can someone please provide an explanation on the difference of the two PHP arrays below and how they are used with a possible output?

$final['a']['b'] = queryX($conn, $id, 'user');
$final['b'] = queryY($conn, $id, 'visitor');

Note that queryX and queryY are functions that contains SQL Queries and returns them as associative arrays.

来源：https://stackoverflow.com/questions/36235787/difference-between-php-arrays-and-possible-output