Convert VARCHAR to date - don't know format in advance

Question

Hi,
If I want to convert varchar to date, but I don't kniow the format of the varchar in advance. For example, it may be '20-MAY-99', '2009-01-10 10:01:00', but it is not known in advance. How can I convert it to date?
Many thanks

Answer 1

You'll have to define a hierarchy of date formats to try. There are some strings that map to many different valid dates depending on the format. The string '01/02/03' might translate to January 2, 2003, January 2, 1903, February 1, 2003, February 1, 1903, February 3, 2001, February 3, 1901, etc.
Assuming you define a hierarchy of formats, you can write a function that tries each format in turn, i.e.
CREATE FUNCTION my_to_date( p_string IN VARCHAR2 )
  RETURN DATE
IS
  l_date_variable DATE;
BEGIN
  l_date_variable := to_date( p_string, <<format 1>> );
  return l_date_variable;
EXCEPTION
  WHEN OTHERS THEN
    BEGIN
      l_date_variable := to_date( p_string, <<format 2>> );
      return l_date_variable;
    EXCEPTION
      WHEN OTHERS THEN
END;You'll need to define the N date formats to try and the order in which to try them.
Justin