Github user mattyb149 commented on a diff in the pull request:

    https://github.com/apache/nifi/pull/1471#discussion_r101091944
  
    --- Diff: 
nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/ExecuteSQL.java
 ---
    @@ -192,31 +192,57 @@ public void process(InputStream in) throws 
IOException {
             try (final Connection con = dbcpService.getConnection();
                 final Statement st = con.createStatement()) {
                 st.setQueryTimeout(queryTimeout); // timeout in seconds
    -            final AtomicLong nrOfRows = new AtomicLong(0L);
    -            if (fileToProcess == null) {
    -                fileToProcess = session.create();
    -            }
    -            fileToProcess = session.write(fileToProcess, new 
OutputStreamCallback() {
    -                @Override
    -                public void process(final OutputStream out) throws 
IOException {
    -                    try {
    -                        logger.debug("Executing query {}", new 
Object[]{selectQuery});
    -                        final ResultSet resultSet = 
st.executeQuery(selectQuery);
    -                        
nrOfRows.set(JdbcCommon.convertToAvroStream(resultSet, out, 
convertNamesForAvro));
    -                    } catch (final SQLException e) {
    -                        throw new ProcessException(e);
    -                    }
    +
    +
    +            logger.debug("Executing query {}", new Object[]{selectQuery});
    +            boolean results = st.execute(selectQuery);
    +            int resultCount = 0;
    +            while(results){
    +                FlowFile resultSetFF;
    +                if(fileToProcess==null)
    +                    resultSetFF = session.create();
    +                else {
    +                    resultSetFF = session.create(fileToProcess);
    +                    resultSetFF = session.putAllAttributes(resultSetFF, 
fileToProcess.getAttributes());
                     }
    -            });
     
    -            // set attribute how many rows were selected
    -            fileToProcess = session.putAttribute(fileToProcess, 
RESULT_ROW_COUNT, String.valueOf(nrOfRows.get()));
    +                final AtomicLong nrOfRows = new AtomicLong(0L);
    +
    +                resultSetFF = session.write(resultSetFF, new 
OutputStreamCallback() {
    +                    @Override
    +                    public void process(final OutputStream out) throws 
IOException {
    +                        try {
    +                            ResultSet resultSet = st.getResultSet();
    +                            
nrOfRows.set(JdbcCommon.convertToAvroStream(resultSet, out, 
convertNamesForAvro));
    +                        } catch (final SQLException e) {
    +                            throw new ProcessException(e);
    +                        }
    +                    }
    +                });
    +
    +                // set attribute how many rows were selected
    +                resultSetFF = session.putAttribute(resultSetFF, 
RESULT_ROW_COUNT, String.valueOf(nrOfRows.get()));
    +
    +                logger.info("{} contains {} Avro records; transferring to 
'success'",
    +                        new Object[]{resultSetFF, nrOfRows.get()});
    +                session.getProvenanceReporter().modifyContent(resultSetFF, 
"Retrieved " + nrOfRows.get() + " rows",
    +                        stopWatch.getElapsed(TimeUnit.MILLISECONDS));
    +                session.transfer(resultSetFF, REL_SUCCESS);
    +                resultCount++;
    +
    +                // are there anymore result sets?
    +                results = st.getMoreResults();
    +            }
     
    -            logger.info("{} contains {} Avro records; transferring to 
'success'",
    -                    new Object[]{fileToProcess, nrOfRows.get()});
    -            session.getProvenanceReporter().modifyContent(fileToProcess, 
"Retrieved " + nrOfRows.get() + " rows",
    -                    stopWatch.getElapsed(TimeUnit.MILLISECONDS));
    -            session.transfer(fileToProcess, REL_SUCCESS);
    +            //If we had at least one result then it's OK to drop the 
original file, but if we had no results then
    +            //  pass the original flow file down the line to trigger 
downstream processors
    +            if(fileToProcess != null) {
    +                if (resultCount > 0) {
    +                    session.remove(fileToProcess);
    +                } else {
    +                    session.transfer(fileToProcess, REL_SUCCESS);
    --- End diff --
    
    An alternative might be to create an empty Avro record (with an empty 
schema if that's possible) and set the attribute for number of rows to zero 
(and/or maybe add an attribute for "result set present" or something if 
needed). Whichever way you go, please add documentation where prudent (in the 
CapabilityDescription for example).


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