[sqlite] why select distinct does not use index?

[Maxim V. Shiyanovsky]

Suppose I have simple table:

CREATE TABLE [profile_data] (

  [profile_id] INTEGER,

  [version] INTEGER);

CREATE INDEX [by_id] ON [profile_data] ([id]);

 

Why 

sqlite> explain query plan

   ...> select distinct(profile_id) from profile_data;

0|0|TABLE profile_data

 

Does not use index?