I have table called `ExamInfo`. In that table the column `Sub1` is of the type `VARCHAR(50)`. The Sub1 column contains **numeric**, **null** and **non-numeric** data. 

I want to select from ExamInfo where the data in Sub1 is greater than 81.

Here is my query: 

```
select * 
from Exam 
where cast(sub1 as int) > 81`.

```

But it fails to cast resulting in an error.