Trying to join two different IDs with AR

[eluser]spmckee[/eluser]
So I have a table called "projects"

Projects
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| project_id | group_id | company_id |
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| 1 | 4 | 2 |
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| 2 | 1 | 2 |
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| 3 | 0 | 1 |
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I then have two other tables "groups" and "companies" that I am wanting to grab info from and include in my result. I can grab the info from one table or the other with join but I can't get the info from both tables at then same time.

Any ideas? Thanks.