That's interesting.
What is the exact precision of each column. How did you put the data in?
Can you give a sample of each index values.


Likely the second query has been found in the DB cache (memory).

I.E. You found it in the first query and stored it in the cache then the second query just pulled the row direct from the cache without any disk access.

You need to reverse the order of the queries after dropping and reimporting the
table and clearing the cache.

The size of the index and differences (or non-differences ) in the data matter also.