Forum Variables

[Genius314]

I need a list of comonly used variables in programming a forum. Also, if possible, put them into categories depending on what they affect (such as members, posts, forums, etc.) Also list what the variable type is.
I have a small list but I'm not sure what else should be there.

Also, how do i have a certain value for each of another variable (like, if i have a 1, 2 and 3 value for userID, then for 1, the value of postcount = 3, for 2, postcount = 5, and 3, postcount =10. Understand what i'm saying?)

And, how can i have PHP search through all the values of a variable and find certain ones? (like search through the variable login for each variable userID and returning what userID values have login = 1)