create table actor(

actor_id int unsigned NOT NULL AUTO_INCREMENT,

name   varchar(16) NOT NULL DEFAULT '',

password    varchar(16) NOT NULL DEFAULT '',

PRIMARY KEY(actor_id),

 KEY   (name)

) ENGINE=InnoDB

insert into actor(name,password) values('cat01','1234567');

insert into actor(name,password) values('cat02','1234567');

insert into actor(name,password) values('ddddd','1234567');

insert into actor(name,password) values('aaaaa','1234567');

mysql> explain select actor_id from actor order by actor_id \G

*************************** 1. row ***************************

      id: 1

 select_type: SIMPLE

    table: actor

     type: index

possible_keys: NULL

     key: PRIMARY

   key_len: 4

     ref: NULL

     rows: 4

    Extra: Using index

1 row in set (0.00 sec)

mysql> explain select actor_id from actor order by password \G

*************************** 1. row ***************************

      id: 1

 select_type: SIMPLE

    table: actor

     type: ALL

possible_keys: NULL

     key: NULL

   key_len: NULL

     ref: NULL

     rows: 4

    Extra: Using filesort

1 row in set (0.00 sec)

mysql> explain select actor_id from actor order by name \G

*************************** 1. row ***************************

      id: 1

 select_type: SIMPLE

    table: actor

     type: index

possible_keys: NULL

     key: name

   key_len: 18

     ref: NULL

     rows: 4

    Extra: Using index

1 row in set (0.00 sec)

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