[PHP] "isset" or "array_key_exists"?

[Nikolay Rastegaev]

Please, answer:

what construction works faster:

   if (  isset ( $result [$i] ["key"] )  )
   {    do something;   }

or

   if (  array_key_exists ( "key", $result [$i] )  )
   {    do something;   }

?

Nikolay