I have a table1(DueDate varchar2(20)). It has thousands of date data in different format with some bad data like characters.

eg. 

```
YYYYMMDD,
MM/DD/YYYY,
MM-DD-YYYY,
M/D/YYYY,
'ABCD'
YYYYMMD,
YYYYMDD,

```

Now I had to get the dates that are past one week overdue. How do I do that?

Thank you for your help.