Could you run the following SQL query directly in your database (using phpMyAdmin or something similar?) and see if the results match what you are looking for?
SELECT m.*, u.*, i.*
FROM Merchants AS m, Updates AS u, Issues AS i
WHERE m.Name LIKE '%$query%'
AND i.MerchantID = m.MerchantID
AND u.IssueID = i.IssueID
When doing that, replace %$query% by a search term included in your database.
Obviously I couldn't test it, but that should be getting you somewhere hopefully =)