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.