I need some kind of a loop

[HakkieDEV]

Hello there,

I would like to know 2 different kind of things.

1)
User should be compared to userstats, all userid's that are missing in user, should be deleted in userstats as well.

2)
userstats should be updated every month with all important (not all) data from user.

user and userstats both have userid for comparison.

Also important to know, can't do a regular loop, since it will try every possible userid, wich is madness, since alot of userid's are already missing (deleted).

Anyone who could help me with the above 2 questions?