describe table would list the column with pre-delete status

Author: alpass163

iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/persistence/schema/ClusterSchemaInfo.java

@@ -1449,7 +1449,7 @@ public DescTableResp descTable(final DescTablePlan plan) {
       }
       return new DescTableResp(
           StatusUtils.OK,
-          tableModelMTree.getUsingTableSchema(databasePath, plan.getTableName()),
+          tableModelMTree.getTableSchemaForDesc(databasePath, plan.getTableName()),
           null,
           null);
     } catch (final MetadataException e) {

iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/persistence/schema/ConfigMTree.java

@@ -1088,6 +1088,36 @@ public TsTable getUsingTableSchema(final PartialPath database, final String tabl
     return newTable;
   }
 
+  /**
+   * The schema to report in DESC. Unlike {@link #getUsingTableSchema}, a column whose deletion is
+   * still pending is kept, so that the user can see which columns exist and are only waiting for
+   * the pending procedure. A pending data type change is applied on top.
+   */
+  public TsTable getTableSchemaForDesc(final PartialPath database, final String tableName)
+      throws MetadataException {
+    final ConfigTableNode node = getTableNode(database, tableName);
+    if (node.getPreAlteredColumns().isEmpty()) {
+      return node.getTable();
+    }
+    final TsTable table = new TsTable(node.getTable());
+    node.getPreAlteredColumns()
+        .forEach(
+            (columnName, dataType) -> {
+              final TsTableColumnSchema columnSchema = table.getColumnSchema(columnName);
+              if (columnSchema == null) {
+                return;
+              }
+              columnSchema.setDataType(dataType);
+              if (columnSchema instanceof FieldColumnSchema) {
+                final FieldColumnSchema fieldColumnSchema = (FieldColumnSchema) columnSchema;
+                fieldColumnSchema.setEncoding(
+                    SchemaUtils.getDataTypeCompatibleEncoding(
+                        dataType, fieldColumnSchema.getEncoding()));
+              }
+            });
+    return table;
+  }
+
   public TableSchemaDetails getTableSchemaDetails(
       final PartialPath database, final String tableName) throws MetadataException {
     final ConfigTableNode node = getTableNode(database, tableName);

iotdb-core/confignode/src/test/java/org/apache/iotdb/confignode/persistence/schema/ConfigMTreeTest.java

@@ -453,6 +453,37 @@ public void testAlterColumnTypeUpdatesCompatibleEncoding() throws Exception {
         root.getTableSchemaDetails(database, table.getTableName()).preAlteredColumns.isEmpty());
   }
 
+  @Test
+  public void testDescKeepsPreDeletedColumns() throws Exception {
+    root = new ConfigMTree(true);
+
+    final PartialPath database = new PartialPath("root.sg");
+    root.setStorageGroup(database);
+    final IDatabaseMNode<IConfigMNode> databaseNode = root.getDatabaseNodeByDatabasePath(database);
+    databaseNode
+        .getAsMNode()
+        .getDatabaseSchema()
+        .setName(PathUtils.unQualifyDatabaseName(database.getFullPath()));
+    databaseNode.getAsMNode().getDatabaseSchema().setIsTableModel(true);
+
+    final TsTable table = new TsTable("table1");
+    table.addColumnSchema(new TagColumnSchema("id", TSDataType.STRING));
+    table.addColumnSchema(
+        new FieldColumnSchema(
+            "measurement", TSDataType.DOUBLE, TSEncoding.GORILLA, CompressionType.SNAPPY));
+    root.preCreateTable(database, table);
+    root.commitCreateTable(database, table.getTableName());
+
+    root.preDeleteColumn(database, table.getTableName(), "measurement", false);
+
+    // DESC keeps a column whose deletion is still pending, so that the user can see it.
+    Assert.assertNotNull(
+        root.getTableSchemaForDesc(database, table.getTableName()).getColumnSchema("measurement"));
+    // A DataNode must not see that column any more.
+    Assert.assertNull(
+        root.getUsingTableSchema(database, table.getTableName()).getColumnSchema("measurement"));
+  }
+
   @Test
   public void testSetTemplate() throws MetadataException {
     root.setStorageGroup(new PartialPath("root.a"));