[incubator-iotdb] 01/01: return empty dataset instead of throw exception

[qi...@apache.org]

This is an automated email from the ASF dual-hosted git repository.

qiaojialin pushed a commit to branch fix_return_null
in repository https://gitbox.apache.org/repos/asf/incubator-iotdb.git

commit 140827d661b7ca153f920567688ac0936b003c27
Author: qiaojialin <64...@qq.com>
AuthorDate: Wed Feb 26 10:07:50 2020 +0800

    return empty dataset instead of throw exception
---
 .../src/main/java/org/apache/iotdb/JDBCExample.java |  2 +-
 .../org/apache/iotdb/jdbc/IoTDBResultMetadata.java  |  5 +----
 .../apache/iotdb/db/qp/executor/PlanExecutor.java   |  6 +++++-
 .../tsfile/read/query/dataset/EmptyDataSet.java     | 21 +++++++++++++++++++++
 4 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/example/jdbc/src/main/java/org/apache/iotdb/JDBCExample.java b/example/jdbc/src/main/java/org/apache/iotdb/JDBCExample.java
index 99a6193..011fba1 100644
--- a/example/jdbc/src/main/java/org/apache/iotdb/JDBCExample.java
+++ b/example/jdbc/src/main/java/org/apache/iotdb/JDBCExample.java
@@ -46,7 +46,7 @@ public class JDBCExample {
       outputResult(resultSet);
       resultSet = statement.executeQuery("select count(*) from root");
       outputResult(resultSet);
-      resultSet = statement.executeQuery("select count(*) from root where time >= 1 and time <= 100 group by ([0, 100], 20ms, 20ms)");
+      resultSet = statement.executeQuery("select count(*) from root where time >= 1 and time <= 100 group by ([0, 100), 20ms, 20ms)");
       outputResult(resultSet);
     }
   }
diff --git a/jdbc/src/main/java/org/apache/iotdb/jdbc/IoTDBResultMetadata.java b/jdbc/src/main/java/org/apache/iotdb/jdbc/IoTDBResultMetadata.java
index 25e88bd..e0af511 100644
--- a/jdbc/src/main/java/org/apache/iotdb/jdbc/IoTDBResultMetadata.java
+++ b/jdbc/src/main/java/org/apache/iotdb/jdbc/IoTDBResultMetadata.java
@@ -59,10 +59,7 @@ public class IoTDBResultMetadata implements ResultSetMetaData {
   }
 
   @Override
-  public int getColumnCount() throws SQLException {
-    if (columnInfoList == null || columnInfoList.isEmpty()) {
-      throw new SQLException("No column exists");
-    }
+  public int getColumnCount() {
     return columnInfoList.size();
   }
 
diff --git a/server/src/main/java/org/apache/iotdb/db/qp/executor/PlanExecutor.java b/server/src/main/java/org/apache/iotdb/db/qp/executor/PlanExecutor.java
index 2cf135d..a489c34 100644
--- a/server/src/main/java/org/apache/iotdb/db/qp/executor/PlanExecutor.java
+++ b/server/src/main/java/org/apache/iotdb/db/qp/executor/PlanExecutor.java
@@ -117,6 +117,7 @@ import org.apache.iotdb.tsfile.read.TsFileSequenceReader;
 import org.apache.iotdb.tsfile.read.common.Field;
 import org.apache.iotdb.tsfile.read.common.Path;
 import org.apache.iotdb.tsfile.read.common.RowRecord;
+import org.apache.iotdb.tsfile.read.query.dataset.EmptyDataSet;
 import org.apache.iotdb.tsfile.read.query.dataset.QueryDataSet;
 import org.apache.iotdb.tsfile.utils.Binary;
 import org.apache.iotdb.tsfile.utils.Pair;
@@ -225,7 +226,10 @@ public class PlanExecutor implements IPlanExecutor {
       throws StorageEngineException, QueryFilterOptimizationException, QueryProcessException,
       IOException {
     QueryDataSet queryDataSet;
-    if (queryPlan instanceof AlignByDevicePlan) {
+    if (queryPlan.getPaths().isEmpty()) {
+      // no time series are selected, return EmptyDataSet
+      queryDataSet = new EmptyDataSet();
+    } else if (queryPlan instanceof AlignByDevicePlan) {
       queryDataSet = new AlignByDeviceDataSet((AlignByDevicePlan) queryPlan, context, queryRouter);
     } else {
       if (queryPlan instanceof GroupByPlan) {
diff --git a/tsfile/src/main/java/org/apache/iotdb/tsfile/read/query/dataset/EmptyDataSet.java b/tsfile/src/main/java/org/apache/iotdb/tsfile/read/query/dataset/EmptyDataSet.java
new file mode 100644
index 0000000..213a7c2
--- /dev/null
+++ b/tsfile/src/main/java/org/apache/iotdb/tsfile/read/query/dataset/EmptyDataSet.java
@@ -0,0 +1,21 @@
+package org.apache.iotdb.tsfile.read.query.dataset;
+
+import java.util.Collections;
+import org.apache.iotdb.tsfile.read.common.RowRecord;
+
+public class EmptyDataSet extends QueryDataSet {
+
+  public EmptyDataSet() {
+    super(Collections.emptyList(), Collections.emptyList());
+  }
+
+  @Override
+  protected boolean hasNextWithoutConstraint() {
+    return false;
+  }
+
+  @Override
+  protected RowRecord nextWithoutConstraint() {
+    return null;
+  }
+}