I have a fair amount of experience using mysql and postgres, but on a
fairly simple level.  My current task is to use "relations" to
simplify some queries.  The table structure is as follows:

____table_1__________
id  data1 data2 data3

____table_2__________
id email misc_data

the relationship is that table 2 may have many records with the same
email address; however, the id field is unique for that record.

Table 1 contains many records for each id.

What I need to do is get all the records in table 1 for a given email
address.  If I wrote it in pretendSQL, I would write it as "SELECT *
FROM table_1 WHERE program IN (SELECT id FROM table_2 WHERE email =
'$given_email_address');

I think this might be a sub-select (again, I'm not experienced in
complex SQL queries).  This is NOT what I want.  Nor do I want to do a
join, if I can avoid it.  A friend gave me a brief explanation, but
he's now unavailable.  But basically, what he said was that you can
set up a relation between the the id and the email address, such that
you can just query table_1 as if the email address was actually a
field.  In other words,
"SELECT * FROM table_1 WHERE email = '$given_email_address';

How would I do this using a relation, and can you give me the short
introduction to what is happening and how I can set this up in
postgres.
I suspect it's fairly simple and straightforward, and I'm pretty
perceptive.  So give me the skinny. :-)