Using MAX on a character column

Question

How do I convert a varchar2 into a number
so I can use the MAX funtion on this?
If I say :
Select MAX(TO_NUMBER(type_code))
from tableAgives an error.
But if I say :
Select MAX(type_code)
from tableAit gives correct output.How is this correct?
Isnt it better to convert type_code into a number and use the
MAX function?

Answer 1

The concept of MAX and MIN apply equally well to strings as to numbers. Look at the first page of the Oxford English Dictionary, and the first word listed (I left my copy at home so I don't know what that word is) , that is equivalent to:
SELECT MIN(word)
FROM english_languageNow, look at the last page, that is:
SELECT MAX(word)
FROM english_languageThis does fall down when your strings are actually representations of numbers (which yours are obviously not), because of the string comparision semantics:
SQL> SELECT *
  2  FROM (SELECT '1' string_num FROM dual UNION ALL
  3        SELECT '2' FROM dual UNION ALL
  4        SELECT '10' FROM DUAL)
  5  ORDER BY string_num;
ST
1
10
2HTH
John