MySQL Gruppér efter ugenummer m/ kolonne med flere dato

prøv:

SELECT weekofyear(forcast_date) AS week_forcast,
   COUNT(forcast_date) AS count_forcast, t2.count_actual
FROM
   t t1 LEFT JOIN (
SELECT weekofyear(actual_date) AS week_actual,
   COUNT(forcast_date) AS count_actual
FROM t
GROUP BY weekOfYear(actual_date)
) AS t2 ON weekofyear(forcast_date)=week_actual
GROUP BY
weekofyear(forcast_date), t2.count_actual

sqlFiddle

Du skal skrive omkring 30 (dine datokolonner) tilbage, og kravet er, at din første datokolonne skal have en tom uge (med et tal på 0), ellers vil joinforbindelserne gå glip af.