JOIN question

I'm looking for the most portable way to do the following,
given these two tables:

Table 1 is called "content" which contains an integer "id" column.
The value of this id is "1" for this example.

Table 2 is called "protection" and keeps track of who can read
and write the content object, so this table may contain multiple
protection settings for a single content object.

Simplifying, to consider my problem, the protection table contains
a column called "contentId", connecting it to the content table id.
This table has three rows in it for three groups that can read it
with contentId set to "1".

If I do the query:

select Content.* from Content,Protection
where (Content.id = Protection.contentId);

I get three rows back, corresponding to each group that has
access to the content. However, I would like to get back
just one row, corresponding to the content that fits the desired
protections.

How do I do this?

Thanks for answering this question for the relative sql newbie.