rating in portal announcement

[RateU]

Yeah. You can join the query there. You can use LEFT_JOIN.

About the $rated condition, you can create the condition after you put the query there.
Basically (I think), your threadratings query is used to check whether an announcement already rated by a user or not. And the value of the user's uid is stored in the $rated variable. So, you need to specify the value first before you use the $rated variable in your code (depends on how you build the query).

For your portal_announcement_rating template, I think you need to use $announcement array.