[...] it is little bit worse. I cannot to distinguish between SELECT\gdesc and TRUNCATE xxx\gdesc . All are valid commands and produce empty result, so result of \gdesc command should be empty result too.
postgres=# truncate table xx\gdesc ┌──────┬──────┐ │ Name │ Type │ ╞══════╪══════╡ └──────┴──────┘ (0 rows)
Hmmm. At least it is better than the previous error.
What about detecting the empty result (eg PQntuples()==0?) and writing "Empty result" instead of the strange looking empty table above? That would just mean skipping the PrintQueryResult call in this case?
PQntuples == 0 every time - the query is not executed.
I am not sure, what is more correct. The "Empty result" string is not used every time in psql. For the case "SELECT;" the empty table is correct. For TRUNCATE and similar command I am not sure. The empty table is maybe unusual, but it is valid - like "SELECT;". The implementation is not problem in any case. The question is what is more natural for users a) the string "Empty result", b) empty table.
I prefer @b due consistency with current behave (that is only reason, I have not any other).