linux - schedule crontab in ubuntu -

i have created cronjob task list in cron.txt file. file contains list of cron jobs executed.

from this, consider  job should run 3 times every day,          * job b should run 4 times in week           * job c should run 8 or 9 times in month. 

i have created crontab execute in every minute. gives more load server. how reduce load server? [**because events scheduled 2 or 3 times in day]. how schedule dynamic crontab this, in linux ubuntu?

edit:

is possible schedule cron in linux, based on value retrieved mysql db instead of running crontab in every minute or every hour ?

(can schedule crontab dynamically based on value retrieved mysql db?)

else,

we run crontab every day midnight schedule times , per schedule times, can run crontab.

[running cron in every minute or every hour unnecessary loading server.]

you should read man page on crontab : (e.g. man crontab)

to edit crontab, need call crontab -e. open editor defined in editor environment variable.

crontab -l list set crontabs. not mean crontab valid.