Use Where clause in calculated column

Dear Experts,

I have following logic to derive Customer and Vendors details in HANA studio using calculated column.

There is two column in the tables (Col1, Col2) based on the col2 values col1 value should be the customer or vendors.

if column col1='D' then col2 is the customer and if col1='K' then col2 is the vendors.

so I need to create calculated column like Col2 where col1='D' so how i will acheive this.

please help

thanks,

Regards,

Karuppiah N