[WIP][Table Model] Support DESCRIBE QUERY for relational metadata extraction

integration-test/src/test/java/org/apache/iotdb/relational/it/query/recent/IoTDBDescribeTableIT.java

@@ -0,0 +1,32 @@
+package org.apache.iotdb.relational.it.query.recent;
+
+import org.apache.iotdb.it.env.EnvFactory;
+import org.apache.iotdb.itbase.category.TableLocalStandaloneIT;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.ResultSetMetaData;
+import java.sql.Statement;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+@Category({TableLocalStandaloneIT.class})
+public class IoTDBDescribeTableIT {
+    @Test
+    public void testDescribeTable() {
+        try (Connection connection = EnvFactory.getEnv().getConnection("TABLE");
+             Statement statement = connection.createStatement()) {
+            statement.execute("CREATE DATABASE test_db");
+            statement.execute("USE test_db");
+            statement.execute("CREATE TABLE t1 (id1 TAG, s1 INT32)");
+            try (ResultSet resultSet = statement.executeQuery("DESCRIBE t1")) {
+                ResultSetMetaData metaData = resultSet.getMetaData();
+                assertEquals("column_name", metaData.getColumnName(1).toLowerCase());
+                assertEquals("column_type", metaData.getColumnName(2).toLowerCase());
+            }
+        } catch (Exception e) {
+            fail(e.getMessage());
+        }
+    }
+}

iotdb-core/antlr/src/main/antlr4/org/apache/iotdb/db/qp/sql/IoTDBSqlParser.g4

@@ -90,6 +90,7 @@ dclStatement
 
 utilityStatement
     : flush | clearCache | setConfiguration | settle | startRepairData | stopRepairData | explain
+    | describe  // <--- Ye line add karo
     | setSystemStatus | showVersion | showFlushInfo | showLockInfo | showQueryResource
     | showQueries | showCurrentTimestamp | killQuery | grantWatermarkEmbedding
     | revokeWatermarkEmbedding | loadConfiguration | loadTimeseries | loadFile
@@ -1239,6 +1240,11 @@ explain
     : EXPLAIN (ANALYZE VERBOSE?)? selectStatement?
     ;
 
+// ---- Describe
+describe
+    : DESCRIBE selectStatement
+    ;
+
 // Set System To readonly/running/error
 setSystemStatus
     : SET SYSTEM TO (READONLY|RUNNING) (ON (LOCAL | CLUSTER))?

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/execution/QueryExecution.java

@@ -252,7 +252,7 @@ private ExecutionResult retry() {
   }
 
   private boolean skipExecute() {
-    return analysis.canSkipExecute(context);
+    return analysis.isFailed() || analysis.isFinishQueryAfterAnalyze();
   }
 
   private void constructResultForMemorySource() {

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/execution/memory/TableModelStatementMemorySourceVisitor.java

@@ -7,7 +7,7 @@
  * "License"); you may not use this file except in compliance
  * with the License.  You may obtain a copy of the License at
  *
- *     http://www.apache.org/licenses/LICENSE-2.0
+ * http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing,
  * software distributed under the License is distributed on an
@@ -34,16 +34,21 @@
 import org.apache.iotdb.db.queryengine.plan.relational.planner.distribute.TableDistributedPlanner;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.AstVisitor;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.CountDevice;
+import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DescribeQuery;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.Explain;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.Node;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.ShowDevice;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.Table;
 
+import org.apache.tsfile.common.conf.TSFileConfig;
 import org.apache.tsfile.enums.TSDataType;
 import org.apache.tsfile.read.common.block.TsBlock;
+import org.apache.tsfile.read.common.block.TsBlockBuilder;
+import org.apache.tsfile.utils.Binary;
 import org.apache.tsfile.utils.Pair;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -130,6 +135,50 @@ public StatementMemorySource visitCountDevice(
         node.getTsBlock(context.getAnalysis()), node.getDataSetHeader());
   }
 
+  @Override
+  public StatementMemorySource visitDescribeQuery(
+      final DescribeQuery node, final TableModelStatementMemorySourceContext context) {
+
+    List<ColumnHeader> columnHeaders = new ArrayList<>();
+    // Jackie's requested lowercase headers
+    columnHeaders.add(new ColumnHeader("column_name", TSDataType.TEXT));
+    columnHeaders.add(new ColumnHeader("column_type", TSDataType.TEXT));
+
+    DatasetHeader datasetHeader = new DatasetHeader(columnHeaders, true);
+
+    List<String> columnNames = new ArrayList<>();
+    List<String> columnTypes = new ArrayList<>();
+
+    context
+        .getAnalysis()
+        .getOutputDescriptor()
+        .getVisibleFields()
+        .forEach(
+            field -> {
+              columnNames.add(field.getName().orElse("unknown"));
+              columnTypes.add(field.getType().toString());
+            });
+
+    TsBlockBuilder builder = new TsBlockBuilder(Arrays.asList(TSDataType.TEXT, TSDataType.TEXT));
+
+    for (int i = 0; i < columnNames.size(); i++) {
+      builder.getTimeColumnBuilder().writeLong(0);
+
+      // Jackie's Fix: No more long paths, just simple class names
+      builder
+          .getColumnBuilder(0)
+          .writeBinary(new Binary(columnNames.get(i), TSFileConfig.STRING_CHARSET));
+
+      builder
+          .getColumnBuilder(1)
+          .writeBinary(new Binary(columnTypes.get(i), TSFileConfig.STRING_CHARSET));
+
+      builder.declarePosition();
+    }
+
+    return new StatementMemorySource(builder.build(), datasetHeader);
+  }
+
   private List<String> mergeExplainResults(
       Map<NodeRef<Table>, Pair<Integer, List<String>>> cteExplainResults,
       List<String> mainExplainResult) {

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/Analysis.java

@@ -257,6 +257,7 @@ public class Analysis implements IAnalysis {
   private boolean emptyDataSource = false;
 
   private boolean isQuery = false;
+  private boolean isDescribe = false;
 
   // SqlParser is needed during query planning phase for executing uncorrelated scalar subqueries
   // in advance (predicate folding). The planner needs to parse and execute these subqueries
@@ -1552,6 +1553,14 @@ public void setInsert(Insert insert) {
     this.insert = insert;
   }
 
+  public void setDescribe(boolean isDescribe) {
+    this.isDescribe = isDescribe;
+  }
+
+  public boolean isDescribe() {
+    return isDescribe;
+  }
+
   public Insert getInsert() {
     return insert;
   }

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/StatementAnalyzer.java

@@ -80,6 +80,7 @@
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.Delete;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DeleteDevice;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DereferenceExpression;
+import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DescribeQuery;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DescribeTable;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DropColumn;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DropDB;
@@ -850,6 +851,21 @@ protected Scope visitExplain(Explain node, Optional<Scope> context) {
       return visitQuery((Query) node.getStatement(), context);
     }
 
+    @Override
+    protected Scope visitDescribeQuery(DescribeQuery node, Optional<Scope> context) {
+      analysis.setFinishQueryAfterAnalyze(true);
+      Scope scope = visitQuery(node.getQuery(), context);
+
+      RelationType outputDescriptor = analysis.getOutputDescriptor();
+      for (Field field : outputDescriptor.getVisibleFields()) {
+        String name = field.getName().orElse("unknown");
+        String type = field.getType().toString();
+      }
+
+      analysis.setDescribe(true);
+      return scope;
+    }
+
     @Override
     protected Scope visitExplainAnalyze(ExplainAnalyze node, Optional<Scope> context) {
       queryContext.setExplainType(ExplainType.EXPLAIN_ANALYZE);

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/sql/ast/AstVisitor.java

@@ -445,7 +445,7 @@ protected R visitRemoveConfigNode(RemoveConfigNode node, C context) {
     return visitStatement(node, context);
   }
 
-  protected R visitDescribeTable(DescribeTable node, C context) {
+  protected R visitDescribeQuery(DescribeQuery node, C context) {
     return visitStatement(node, context);
   }
 
@@ -545,6 +545,11 @@ protected R visitGroupBy(GroupBy node, C context) {
     return visitNode(node, context);
   }
 
+  protected R visitDescribeTable(
+      org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DescribeTable node, C context) {
+    return visitStatement(node, context);
+  }
+
   protected R visitGroupingElement(GroupingElement node, C context) {
     return visitNode(node, context);
   }

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/sql/ast/DescribeQuery.java

@@ -0,0 +1,81 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.iotdb.db.queryengine.plan.relational.sql.ast;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.tsfile.utils.RamUsageEstimator;
+
+import java.util.List;
+import java.util.Objects;
+
+import static java.util.Objects.requireNonNull;
+
+public class DescribeQuery extends Statement {
+
+  private static final long INSTANCE_SIZE =
+      RamUsageEstimator.shallowSizeOfInstance(DescribeQuery.class);
+
+  private final Query query;
+
+  public DescribeQuery(NodeLocation location, Query query) {
+    super(requireNonNull(location, "location is null"));
+    this.query = requireNonNull(query, "query is null");
+  }
+
+  public Query getQuery() {
+    return query;
+  }
+
+  @Override
+  public <R, C> R accept(AstVisitor<R, C> visitor, C context) {
+    return visitor.visitDescribeQuery(this, context);
+  }
+
+  @Override
+  public List<Node> getChildren() {
+    return ImmutableList.of(query);
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) return true;
+    if (obj == null || getClass() != obj.getClass()) return false;
+    DescribeQuery that = (DescribeQuery) obj;
+    return Objects.equals(query, that.query);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(query);
+  }
+
+  @Override
+  public String toString() {
+    return "DescribeQuery{" + "query=" + query + '}';
+  }
+
+  @Override
+  public long ramBytesUsed() {
+    long size = INSTANCE_SIZE;
+    size += AstMemoryEstimationHelper.getEstimatedSizeOfNodeLocation(getLocationInternal());
+    size += AstMemoryEstimationHelper.getEstimatedSizeOfAccountableObject(query);
+    return size;
+  }
+}

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/sql/util/SqlFormatter.java

@@ -34,6 +34,7 @@
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.CreateTopic;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.CreateView;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.Delete;
+import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DescribeTable;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DropColumn;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DropDB;
 import org.apache.iotdb.db.queryengine.plan.relational.sql.ast.DropFunction;
@@ -1711,6 +1712,13 @@ private void appendTableFunctionArguments(List<TableFunctionArgument> arguments,
       }
     }
 
+    @Override
+    protected Void visitDescribeTable(DescribeTable node, Integer indent) {
+      builder.append("DESCRIBE ");
+      builder.append(node.getTable().toString());
+      return null;
+    }
+
     @Override
     public Void visitTableArgument(TableFunctionTableArgument node, Integer indent) {
       Relation relation = node.getTable();

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/transformation/datastructure/tv/ElasticSerializableTVList.java

@@ -25,6 +25,7 @@
 import org.apache.tsfile.block.column.Column;
 import org.apache.tsfile.common.conf.TSFileConfig;
 import org.apache.tsfile.enums.TSDataType;
+import org.apache.tsfile.read.common.block.column.TimeColumn;
 import org.apache.tsfile.utils.Binary;
 
 import java.io.IOException;
@@ -183,16 +184,16 @@ public void putColumn(Column timeColumn, Column valueColumn) throws IOException
         consumed = total;
         if (begin == 0) {
           // No need to copy if the columns do not split
-          insertedTimeColumn = timeColumn;
+          insertedTimeColumn = ensureTimeColumn(timeColumn);
           insertedValueColumn = valueColumn;
         } else {
-          insertedTimeColumn = timeColumn.getRegionCopy(begin, consumed);
+          insertedTimeColumn = ensureTimeColumn(timeColumn.getRegionCopy(begin, consumed));
           insertedValueColumn = valueColumn.getRegionCopy(begin, consumed);
         }
       } else {
         consumed = internalTVListCapacity - pointCount % internalTVListCapacity;
         // Construct sub-regions
-        insertedTimeColumn = timeColumn.getRegionCopy(begin, consumed);
+        insertedTimeColumn = ensureTimeColumn(timeColumn.getRegionCopy(begin, consumed));
         insertedValueColumn = valueColumn.getRegionCopy(begin, consumed);
       }
 
@@ -284,4 +285,15 @@ public SerializableTVList get(int targetIndex) throws IOException {
       return internalTVList.get(targetIndex);
     }
   }
+
+  private Column ensureTimeColumn(Column column) {
+    if (column instanceof TimeColumn) {
+      return column;
+    }
+    long[] times = new long[column.getPositionCount()];
+    for (int i = 0; i < times.length; i++) {
+      times[i] = column.getLong(i);
+    }
+    return new TimeColumn(column.getPositionCount(), times);
+  }
 }

iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/schema/column/ColumnHeaderConstant.java

@@ -349,6 +349,9 @@ private ColumnHeaderConstant() {
   public static final String SHOW_CONFIGURATIONS_DEFAULT_VALUE = "default_value";
   public static final String SHOW_CONFIGURATIONS_DESCRIPTION = "description";
 
+  public static final String COLUMN_NAME_DUCKDB = "column_name";
+  public static final String COLUMN_TYPE_DUCKDB = "column_type";
+
   public static final List<ColumnHeader> lastQueryColumnHeaders =
       ImmutableList.of(
           new ColumnHeader(TIMESERIES, TSDataType.TEXT),
@@ -708,14 +711,14 @@ private ColumnHeaderConstant() {
 
   public static final List<ColumnHeader> describeTableColumnHeaders =
       ImmutableList.of(
-          new ColumnHeader(COLUMN_NAME, TSDataType.TEXT),
-          new ColumnHeader(COLUMN_DATA_TYPE, TSDataType.TEXT),
+          new ColumnHeader(COLUMN_NAME_DUCKDB, TSDataType.TEXT),
+          new ColumnHeader(COLUMN_TYPE_DUCKDB, TSDataType.TEXT),
           new ColumnHeader(COLUMN_CATEGORY, TSDataType.TEXT));
 
   public static final List<ColumnHeader> describeTableDetailsColumnHeaders =
       ImmutableList.of(
-          new ColumnHeader(COLUMN_NAME, TSDataType.TEXT),
-          new ColumnHeader(COLUMN_DATA_TYPE, TSDataType.TEXT),
+          new ColumnHeader(COLUMN_NAME_DUCKDB, TSDataType.TEXT),
+          new ColumnHeader(COLUMN_TYPE_DUCKDB, TSDataType.TEXT),
           new ColumnHeader(COLUMN_CATEGORY, TSDataType.TEXT),
           new ColumnHeader(STATUS, TSDataType.TEXT),
           new ColumnHeader(COMMENT, TSDataType.TEXT));