A Tcl error will be returned if pgtcl was unable to obtain a backend
response. Otherwise, a query result object is created and a handle for
it is returned. This handle can be passed to pg_result
to obtain the results of the query.
pg_exec submits a query to the PostgreSQL backend and returns a result.
Query result handles start with the connection handle and add a period
and a result number.
Note that lack of a Tcl error is not proof that the query succeeded!
An error message returned by the backend will be processed
as a query result with failure status, not by generating a Tcl error