How to set initial default value from SQL query in a context segment

Hello, Im triying to set a default value inside a descriptive flexfield inside a context sentitive segment.

The flexfield is inside the shipment line module, as we are triying to access the attribute_char1 of the transferOrderLine that precede the shipment line.

We did set the value-set for the field, succesfully, as a simple select from PJF_PROJECTS_ALL_B project that are active at the moment of the shipment.

The problem comes with the default value, the default value we are trying to set is the ATTRIBUTE_CHAR1 of the transfer order lines that precede the shipment, our first attempt was to do a SQL Query as follows: