elasticsearch - _all field in match phrase prefix query -

my documents have field product_code containing string value pc00xxa x replaced digit 1..9. i'm expecting result of 9 documents phrase prefix query:

{   "query": {     "match": {       "_all": {         "query": "pc001",         "type": "phrase_prefix"       }     }   } } 

... result empty. using product_code instead of _all, expected 9 documents.

using prefix query instead of phrase prefix query seems work expected both _all , product_code fields. following query gives me 9 documents:

{   "query": {     "prefix": {       "_all": {         "value": "pc001"       }     }   } } 

elasticsearch documentation says "the match_phrase_prefix same match_phrase, except allows prefix matches on last term in text". in case have 1 term in query expect work prefix.

how phrase prefix query differ prefix query when query contains single term? , why use of _all gives me fewer results specifying field name explicitly?