dbClearResult() returns TRUE, invisibly, for result sets obtained from
both dbSendQuery()
and dbSendStatement().
An attempt to close an already closed result set issues a warning
in both cases.
Specification
dbClearResult() frees all resources associated with retrieving
the result of a query or update operation.
The DBI backend can expect a call to dbClearResult() for each
dbSendQuery() or dbSendStatement() call.