SELECT SCELTA, SUM(TOT) AS TOT FROM (
SELECT scelta1 AS SCELTA, COUNT(*) AS TOT FROM tabella GROUP BY scelta1
UNION ALL
SELECT scelta2 AS SCELTA, COUNT(*) AS TOT FROM tabella GROUP BY scelta2
UNION ALL
SELECT scelta3 AS SCELTA, COUNT(*) AS TOT FROM tabella GROUP BY scelta3
) AS TX GROUP BY SCELTA ORDER BY 1