Issue with OBIEE Double Column Prompt Default Value

User_NRSQX

I have a a column prompt based on a double column (ID and descriptor) in OBIEE.

I would like to set a default value based on a session variable.

If I use descriptor value, the prompt works but query fails.

If I use ID value, query works, but after the query finishes, ID value is displayed in prompt instead of descriptor value.

What format should I use?

Thanks very much

Qing