Join two tables and create a new one in SQL
You need to UNION ALL the two table entries
Then take the SUM(Category) by GROUP BY ID, Name


So the query will be

SELECT ID, Name, SUM(Category) AS Category
FROM  (
    SELECT ID, Name, Category FROM Table1 
    UNION ALL
    SELECT ID, Name, Category FROM Table2
) GROUP BY ID, Name


You can insert the entries into the third table.