Questo:
SELECT SUM(CASE WHEN Col1 = 'false' THEN 1 ELSE 0 END) AS Col1
, SUM(CASE WHEN Col2 = 'false' THEN 1 ELSE 0 END) AS Col2
, SUM(CASE WHEN Col3 = 'false' THEN 1 ELSE 0 END) AS Col3
, SUM(CASE WHEN Col4 = 'false' THEN 1 ELSE 0 END) AS Col4
, SUM(CASE WHEN Col5 = 'false' THEN 1 ELSE 0 END) AS Col5
FROM T_myTable