I'm having a dilemma and I know there has to be a simple solution I just cant seem to wrap my head around it.  I am creating a real estate investor database in which I have specific zip codes each investor is interested in purchasing properties.  A single investor may have anywhere from 1 to 240 zipcodes on his want to buy in list and that's just in the Houston area.  Not to mention if I wanted to take it national.  I want to be able to have all desired databases for each investor and then be able to search by a certain zipcode so I can get a short list of all investors in that specific area.  Please help, Ive spent a hundred hours trying to find a solution for this.

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Reply from Alex Hedley:

You will want 1 table to store all your addresses.
1 table to store your investors
You then need a Junction table to store the investors zip codes
you can then create a form to add a zip for an investor
now you can join the 3 tables and filter by zip or investor to get the required lists.

See this blog post for more info.