Clear cache in heidiSQL

is there any way to clear cache in heidisql? i want to calculate query time but it is always 0,000 sec

You mean the server side query cache - yes you can disable it per SQL_NO_CACHE keyword in any query:

SELECT SQL_NO_CACHE title FROM book ...

Note for debugging purposes you can also check the query profiler in the right helpers box, which will give you more accurate times: