Question about query

[Jin Hui]

Hi,

I have a query like
select id from atable where truncate(c1/1000000) = 321

I learned that following query has the same function
select id from atable where c1 like '321______'

I'd like to know which is faster. Or anyone know how to do integer division
in MySQL faster.

And if I make a index on c1 or a index on c1/1000000, which index will
increase the query speed, or none index is helpful. 

Thanks!

Best Regards,
Jin Hui