This is not an urgent problem, but it has always intrigued me...
It's simplified case, but it makes the point. Let us assume that we have a
create table T (id unsigned int unique, name char(10));
create index i_name on T(name);
Let's insert into it say 5 mil rows with name field being just say 5
distinct values AAA, BBB, CCC, DDD, EEE.
Now the question. Why a query like
select distinct name from T;
takes about 3 sec to return just a bunch of rows?
As I understand it, index contains all these 5 values, so just simple
lookup into index should take fractions of a second.
Can anyone comment on this? MySQL team?