Fix nested query and type conversion in MySQL, remove unused codes (#4738)

apm-commons/apm-datacarrier/src/main/java/org/apache/skywalking/apm/commons/datacarrier/consumer/ConsumerPoolFactory.java

@@ -21,7 +21,6 @@ package org.apache.skywalking.apm.commons.datacarrier.consumer;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.Callable;
-import org.apache.skywalking.apm.commons.datacarrier.buffer.Channels;
 
 /**
  * Consumer Pool Factory provides global management for all Consumer Pool.
@@ -29,10 +28,10 @@ import org.apache.skywalking.apm.commons.datacarrier.buffer.Channels;
 public enum ConsumerPoolFactory {
     INSTANCE;
 
-    private Map<String, ConsumerPool> pools;
+    private final Map<String, ConsumerPool> pools;
 
     ConsumerPoolFactory() {
-        pools = new HashMap<String, ConsumerPool>();
+        pools = new HashMap<>();
     }
 
     public synchronized boolean createIfAbsent(String poolName, Callable<ConsumerPool> creator) throws Exception {
@@ -48,43 +47,4 @@ public enum ConsumerPoolFactory {
         return pools.get(poolName);
     }
 
-    /**
-     * Default pool provides the same capabilities as DataCarrier#consume(IConsumer, 1), which alloc one thread for one
-     * DataCarrier.
-     */
-    public static final ConsumerPool DEFAULT_POOL = new ConsumerPool() {
-        private Map<Channels, ConsumeDriver> allDrivers = new HashMap<Channels, ConsumeDriver>();
-
-        @Override
-        synchronized public void add(String name, Channels channels, IConsumer consumer) {
-            if (!allDrivers.containsKey(channels)) {
-                ConsumeDriver consumeDriver = new ConsumeDriver(name, channels, consumer, 1, 20);
-                allDrivers.put(channels, consumeDriver);
-            }
-        }
-
-        /**
-         * Always return true.
-         */
-        @Override
-        public boolean isRunning(Channels channels) {
-            return true;
-        }
-
-        @Override
-        public void close(Channels channels) {
-            ConsumeDriver driver = allDrivers.get(channels);
-            if (driver != null) {
-                driver.close(channels);
-            }
-        }
-
-        @Override
-        public void begin(Channels channels) {
-            ConsumeDriver driver = allDrivers.get(channels);
-            if (driver != null) {
-                driver.begin(channels);
-            }
-        }
-    };
 }

oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/query/type/TopNEntity.java

@@ -38,6 +38,6 @@ public class TopNEntity {
     public TopNEntity(SelectedRecord record) {
         this.name = record.getName();
         this.id = record.getId();
-        this.value = Long.parseLong(record.getValue());
+        this.value = Double.valueOf(record.getValue()).longValue();
     }
 }

oap-server/server-storage-plugin/storage-jdbc-hikaricp-plugin/src/main/java/org/apache/skywalking/oap/server/storage/plugin/jdbc/h2/dao/H2AggregationQueryDAO.java

@@ -68,7 +68,7 @@ public class H2AggregationQueryDAO implements IAggregationQueryDAO {
             });
         }
         sql.append(" group by ").append(Metrics.ENTITY_ID);
-        sql.append(") order by value ")
+        sql.append(")  as T order by value ")
            .append(metrics.getOrder().equals(Order.ASC) ? "asc" : "desc")
            .append(" limit ")
            .append(metrics.getTopN());