Why tb1.Name=tb2.Name does not use index on Name

[cy163]

Hello ALL,

I did the following query. the EXPLAIN result showed 'NULL' in the 'key' colume, meaning that NONE of indexes have been used. However, indexes have been created on Name fields for both tb1 and tb2. I wonder why MySQL does not use the indexes to speed up the query. Is there any way to make the query faster?

EXPLAIN SELECT
         tb1.Name
FROM
         tb1, tb2
WHERE
         tb1.Name = tb2.Name;