@Override
    public final boolean combine(Metrics metrics) {
        AvgLabeledFunction longAvgMetrics = (AvgLabeledFunction) metrics;
        summation.append(longAvgMetrics.summation);
        count.append(longAvgMetrics.count);
        return true;
    }
Service ID is required for sort query.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/meter/function/avg/AvgLabeledFunction.java