Combine multiples table to a new one
I think you are looking for a FULL OUTER JOIN:

SELECT COALESCE(a.id,b.id,c.id), COALESCE(a.col1,'NULL'), COALESCE(b.col2,'NULL'), COALESCE(c.col3,'NULL')
  FROM table1 a
  FULL OUTER JOIN table2 b ON a.id=b.id
  FULL OUTER JOIN table3 c ON b.id=c.id;


or, if you want blanks instead of strings:

SELECT COALESCE(a.id,b.id,c.id), a.col1, b.col2, c.col3
  FROM table1 a
  FULL OUTER JOIN table2 b ON a.id=b.id
  FULL OUTER JOIN table3 c ON b.id=c.id;