SELECT * FROM (
SELECT 1 AS ticked, col1, col2 FROM table1 INNER JOIN table2 USING (col3))
UNION
SELECT 0 AS ticked, col1, col2 FROM table1)
)AS combined_table /*derived tables need a unique name*/
GROUP BY col1 /*group by the unique col1 to stop duplicates*/
ORDER BY ticked DESC
taken from,
http://dev.mysql.com/doc/refman/5.0/en/union.html
