SELECT C2 FROM(
  -- Branch 1: c6='V6' AND C4='25' AND C5 IN(...) AND c7='v7a'
  SELECT C2 FROM t1
  WHERE C2 IS NOT NULL AND C2 <>''
    AND C6 IN ('V6') AND C4='25' AND C5 IN ('1238','1296',...)
    AND C7 IN ('v7a')
  UNION ALL
  -- Branch 2: c4='4' AND C5 IN(...)
  SELECT C2 FROM t1
  WHERE C2 IS NOT NULL AND C2 <>''
    AND C4 ='4' AND 5 IN ('10135269','10144642')
  UNION ALL
  -- Branch 3: c4='20' AND C5 IN(...)
  SELECT C2 FROM t1
  WHERE C2 IS NOT NULL AND c2 <>''
  AND C4 ='20' AND C5 IN ('2000000085', '2000000086',...)
  UNION ALL
  -- Branches 4-7: NOT IN branches, split in the same way.
  SELECT C2 FROM t1
  WHERE C2 IS NOT NULL AND c2 <>''
  AND C4 ='25' AND C5 NOT IN ('1238','1296',...)
  UNION ALL
  -- ...other NOT IN branches...
) AS sub;