Very simple self-join, yet indeces ignored?

Got a noob question. Say I create the following table:

temp1

up, varchar(15)

dn, varchar(15)

and I add a couple of indeces:

create table temp1 (up varchar(15), dn varchar(15), index id1(up), index id2(dn))

After I populate the table with some random data, I do the following explain select

explain select * from temp1 as t1, temp1 as t2 where t1.up = t2.up

and get

+----+-------------+-------+------+---------------+------+---------+------+------+-------------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra       |
+----+-------------+-------+------+---------------+------+---------+------+------+-------------+
|  1 | SIMPLE      | t1    | ALL  | id1           | NULL | NULL    | NULL |    4 |             |
|  1 | SIMPLE      | t2    | ALL  | id1           | NULL | NULL    | NULL |    3 | Using where |
+----+-------------+-------+------+---------------+------+---------+------+------+-------------+

Why isn't the optimizer using the keys?! I must be missing something very simple . . .

(I'm asking this question because a similar query with th开发者_StackOverflowe tables I'm actually using (700K rows) is running awfully slow, and I'm guessing it has to do with indeces).

Thanks for the help!

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Since you select all the rows from temp t1 (and almost all from t2) - mysql decides to use fullscan, due to it is more suitable in such case.

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Correct me if i'm wrong, but this would return ALL values of your table temp1. It would not help you to use any indexes, because you are not looking for a subset of anything.