Flat file loading issues

Hi,

I loaded one flat file to my HANA System and created a table.

Now if i make any changes in my flat file not changing the primary key and try to update the table in HANA, i am getting the error :

error : Unique Constraint Violated

Secondly, while loading flat file i am able to convert data type of all the fields.

But when i convert a data type for my date column from NVARCHAR to DATE, i am getting another error.