continuous insert or update large data ?

i have my users table containing 1miliions data and now i want to make one audience table on which i want to perform some operations

now what i need is all my users get inserted into audience table and once inserted I need continuous updations on audience table because user table may gets updated in future

so like i need one background task which will fetch informations from user table and then insert all the data onto audience table

new data gets inserted old data gets updated

what approach would you suggest for this (just a discussion as I need some better and senior level ideas)