Joining two database tables into one
I would use a view. Just prepare a select in the form of:

SELECT Field1, Field2, Field3, Field4, null as Field5, null as Field6
  FROM Table1

UNION 

SELECT Field1, null, Field3, Field4, Field5, Field6
  FROM Table2;


You can refine the select to filter or extend, as you like. When you're satisfied, just define a view as:

CREATE VIEW MergedTable AS 
SELECT Field1, Field2, Field3, Field4, null as Field5, null as Field6
  FROM Table1

UNION 

SELECT Field1, null, Field3, Field4, Field5, Field6
  FROM Table2;


Then you can always run your selects against the view, nearly as it was a table.

SELECT * FROM MergedTable;