text: IMPORT DTREE FROM FILE 'rst.txt';
  
  CREATE STREAM R(A int, B float) FROM FILE 'R.dat' LINE DELIMITED CSV;
  CREATE TABLE S(A int, C int, E float, extra int) FROM FILE 'S.dat' LINE DELIMITED CSV;
  CREATE STREAM T(C int, D float) FROM FILE 'T.dat' LINE DELIMITED CSV;
  
  SELECT SUM(A*B*C*D) FROM R NATURAL JOIN S NATURAL JOIN T;