when making a forum with php + mysq

when you view a thread, its grabbing a bunch of posts that belong to it, but each post has information about the user who posted it

should for each post it opens the user database and grabs the information? or is there another way to do this? how do forums usually handle this?

should for each post it opens the user database and grabs the information? or is there another way to do this? how do forums usually handle this?

That depends on the query you have used, it will only return as much, or as little data you have set it to return.

but isn't repetitively querying the database bad? i don't know...
it would only be name posts and signature stuff like that

Not necessarily. Certainly, if you can pull all the data back in a single query it can be easier, but making a second call to get limited data can be more efficient than dragging more data back than needed.

Some forums use cache mechanism to serve frequently visited content.
Go through the source code of PHPBB (It is open-source), you will learn a lot of best practices.

I'd recommend having user's information and stuff stored in a 'members' table.
Thread information stored in 'threads' table.
Post information (replies) stored in a 'posts' table.

Table structure for posts:

Column:
postID------threadID---postContent---postAuthorUID---postDate

Table structure for threads:

Column:
threadID---replies---original_poster---date---otherstuff

Table structure for members:
Column:
userID---postcount---avatar---username---realname---age---...

Then simple reference things like on the post it will take postAuthorUID and look up that userID in the members table, and display anything it wants about the member.

Very, very vague approach, I know. I can help you more, as I'm making a forum from scratch with PHP & MySQL.

Hope I could help