src/interfaces/ecpg/README.dynSQL

descriptor statements have the following shortcomings

- input descriptors (USING DESCRIPTOR <name>) are not supported

Reason: to fully support dynamic SQL the frontend/backend communication

should change to recognize input parameters.

Since this is not likely to happen in the near future and you

can cover the same functionality with the existing infrastructure

(using s[n]printf), I'll leave the work to someone else.