MySQL View from different database with the same table schema
Simply reference whatever databases you want.  Note the "db.tbl" syntax:

CREATE VIEW ...
    AS
    SELECT ...
        FROM sales_2014.blah AS x
        JOIN sales_2015.blah AS y ON ...


Similarly, you could use UNION ALL.

CREATE OR REPLACE VIEW
    AS all_sales
        SELECT * FROM 2014.sales
    UNION ALL
        SELECT * FROM 2015.sales;


For 'sanity', you might want to create a new database to store the VIEWs in.  You might call it sales_all.