Is a query with UNIX_TIMESTAMP using indexes in mysql? If I use 

.. WHERE UNIX_TIMESTAMP(`some_timestamp`)&gt;NOW()


in a SELECT, does this query still make use on an index, set on some_timestamp ?
No. Up to now, the optimizer in all MySQL versions cannot use an index for such a condition. It is not sargable

If you want it to be able to use indexes, you'll have to use a function to rewrite/reverse your condition so no function is applied on the column:

WHERE some_timestamp &gt; ReverseFunctionOf_UNIX_TIMESTAMP( NOW() )


What to use, depends on the column some_timestamp datatype. 



If it is a TIMESTAMP, you can simply use 

WHERE some_timestamp&gt; NOW()




If some_timestamp is an INT that stores Unix timestamps (seconds since '1970-01-01 00:00:00'), I think you had the correct function but in the wrong place. You should use:

WHERE some_timestamp &gt; UNIX_TIMESTAMP( NOW() )


or the equivalent:

WHERE some_timestamp &gt; UNIX_TIMESTAMP()




Check MySQL documentation: DATE and TIME functions