SQL - sum columns with same name from diferent tables
If they're all in the same order, you can do it easily like this,

SELECT t.id, sum(c1), sum(c2)
FROM (
  SELECT *
  FROM tbl1
  UNION ALL ( TABLE tbl2 )
  UNION ALL ( TABLE tbl3 )
) AS t
GROUP BY t.id
ORDER BY 1;


If they're in different orders just replace TABLE tbl2 with SELECT id, c1, c2 FROM tbl2 (they're the same thing).