Very simple mysql query not using index -

sorting of mysql table not use index , don't know why.

i've got:

create table if not exists `test` (   `a` int(11) not null,   `b` int(11) not null,   key `kk` (`a`) ) engine=myisam default charset=utf8; 

and this:

explain select *  test order 

as this

explain select *  test use index ( kk )  order 

gives me this:

id select_type table type possible_keys key  key_len ref  rows  1  simple      test   null          null null    null 10009 using filesort 

i'd not see filesort, , use key kk sort table. doing wrong?

---

thank posts guys, answer question! however, not undestand meant "table scan" , "filesort"? if selecting fields , rows of table, isn't faster sort table 1 column walking in o(n) internal tree of index of column (and looking in table file columns requested, in o(1) each row => index file stores each row's physical position in table file, or?), sort e.g. quick sort in o(n * log n) (potentially) randomly stored rows in table file, without touching index? guess understanding of how indexes work in mysql wrong.

1. you're selecting rows
2. you're selecting columns

following said above - mysql estimates more efficient use full scan.

to using index need add where limit reasonable number of rows returned (say 50)