array_merge can take variable number of arguments, so with a little call_user_func_array trickery you can pass your $result
array to it:
$merged = call_user_func_array('array_merge', $result);
This basically run like if you would have typed:
$merged = array_merge($result[0], $result[1], .... $result[n]);
Update:
Now with 5.6, we have the ...
operator to unpack arrays to arguments, so you can:
$merged = array_merge(...$result);
And have the same results. *
* The same results as long you have integer keys in the unpacked array, otherwise you’ll get an E_RECOVERABLE_ERROR : type 4096 -- Cannot unpack array with string keys
error.