[Feature] implement transpose command as in the roadmap #4786

core/src/main/java/org/opensearch/sql/analysis/Analyzer.java

@@ -99,6 +99,7 @@
 import org.opensearch.sql.ast.tree.StreamWindow;
 import org.opensearch.sql.ast.tree.SubqueryAlias;
 import org.opensearch.sql.ast.tree.TableFunction;
+import org.opensearch.sql.ast.tree.Transpose;
 import org.opensearch.sql.ast.tree.Trendline;
 import org.opensearch.sql.ast.tree.UnresolvedPlan;
 import org.opensearch.sql.ast.tree.Values;
@@ -703,6 +704,11 @@ public LogicalPlan visitML(ML node, AnalysisContext context) {
     return new LogicalML(child, node.getArguments());
   }
 
+  @Override
+  public LogicalPlan visitTranspose(Transpose node, AnalysisContext context) {
+    throw getOnlyForCalciteException("Transpose");
+  }
+
   @Override
   public LogicalPlan visitBin(Bin node, AnalysisContext context) {
     throw getOnlyForCalciteException("Bin");

core/src/main/java/org/opensearch/sql/ast/AbstractNodeVisitor.java

@@ -86,6 +86,7 @@
 import org.opensearch.sql.ast.tree.StreamWindow;
 import org.opensearch.sql.ast.tree.SubqueryAlias;
 import org.opensearch.sql.ast.tree.TableFunction;
+import org.opensearch.sql.ast.tree.Transpose;
 import org.opensearch.sql.ast.tree.Trendline;
 import org.opensearch.sql.ast.tree.Values;
 import org.opensearch.sql.ast.tree.Window;
@@ -282,6 +283,10 @@ public T visitReverse(Reverse node, C context) {
     return visitChildren(node, context);
   }
 
+  public T visitTranspose(Transpose node, C context) {
+    return visitChildren(node, context);
+  }
+
   public T visitChart(Chart node, C context) {
     return visitChildren(node, context);
   }

core/src/main/java/org/opensearch/sql/ast/tree/Transpose.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.ast.tree;
+
+import com.google.common.collect.ImmutableList;
+import java.util.List;
+import lombok.*;
+import org.opensearch.sql.ast.AbstractNodeVisitor;
+import org.opensearch.sql.ast.expression.Argument;
+
+/** AST node represent Transpose operation. */
+@Getter
+@Setter
+@ToString
+@EqualsAndHashCode(callSuper = false)
+@RequiredArgsConstructor
+public class Transpose extends UnresolvedPlan {
+  private final @NonNull java.util.Map<String, Argument> arguments;
+  private UnresolvedPlan child;
+
+  public Integer getMaxRows() {
+    Integer maxRows = 5;
+    if (arguments.containsKey("number")) {
+      try {
+        maxRows = Integer.parseInt(arguments.get("number").getValue().toString());
+      } catch (NumberFormatException e) {
+        // log warning and use default
+        maxRows = 5;
+      }
+    }
+    return maxRows;
+  }
+
+  public String getColumnName() {
+    String columnName = "column";
+    if (arguments.containsKey("columnName")) {
+      columnName = arguments.get("columnName").getValue().toString();
+    }
+    return columnName;
+  }
+
+  @Override
+  public Transpose attach(UnresolvedPlan child) {
+    this.child = child;
+    return this;
+  }
+
+  @Override
+  public List<UnresolvedPlan> getChild() {
+    return this.child == null ? ImmutableList.of() : ImmutableList.of(this.child);
+  }
+
+  @Override
+  public <T, C> T accept(AbstractNodeVisitor<T, C> nodeVisitor, C context) {
+    return nodeVisitor.visitTranspose(this, context);
+  }
+}

core/src/main/java/org/opensearch/sql/calcite/CalciteRelNodeVisitor.java

@@ -29,6 +29,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Streams;
+import java.util.AbstractMap;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.BitSet;
@@ -696,6 +697,110 @@ public RelNode visitReverse(
     return context.relBuilder.peek();
   }
 
+  @Override
+  public RelNode visitTranspose(
+      org.opensearch.sql.ast.tree.Transpose node, CalcitePlanContext context) {
+    visitChildren(node, context);
+    Integer maxRows = node.getMaxRows();
+    if (maxRows == null || maxRows <= 0) {
+      throw new IllegalArgumentException("maxRows must be a positive integer");
+    }
+    String columnName = node.getColumnName();
+    // Get the current schema to transpose
+    RelNode currentNode = context.relBuilder.peek();
+    List<String> fieldNames = currentNode.getRowType().getFieldNames();
+    List<RelDataTypeField> fields = currentNode.getRowType().getFieldList();
+    if (fieldNames.isEmpty()) {
+      return currentNode;
+    }
+
+    //  Add row numbers to identify each row uniquely
+    RexNode rowNumber =
+        context
+            .relBuilder
+            .aggregateCall(SqlStdOperatorTable.ROW_NUMBER)
+            .over()
+            .rowsTo(RexWindowBounds.CURRENT_ROW)
+            .as("__row_id__");
+    context.relBuilder.projectPlus(rowNumber);
+
+    // Unpivot the data - convert columns to rows
+    // Each field becomes a row with: row_id, column, value
+    List<String> measureColumns = ImmutableList.of("value");
+    List<String> axisColumns = ImmutableList.of(columnName);
+
+    // Create the unpivot value mappings
+    List<Map.Entry<List<RexLiteral>, List<RexNode>>> valueMappings = new ArrayList<>();
+    RelDataType varcharType =
+        context.rexBuilder.getTypeFactory().createSqlType(SqlTypeName.VARCHAR);
+
+    for (String fieldName : fieldNames) {
+      if (fieldName.equals("__row_id__")) {
+        continue; // Skip the row number column
+      }
+
+      // Create the axis value (column name as literal)
+      RexLiteral columnNameLiteral = context.rexBuilder.makeLiteral(fieldName);
+      List<RexLiteral> axisValues = ImmutableList.of(columnNameLiteral);
+
+      // Create the measure value (field expression cast to VARCHAR)
+      RexNode fieldValue = context.relBuilder.field(fieldName);
+      RexNode castValue = context.rexBuilder.makeCast(varcharType, fieldValue, true);
+      List<RexNode> measureValues = ImmutableList.of(castValue);
+
+      // Create the mapping entry
+      valueMappings.add(new AbstractMap.SimpleEntry<>(axisValues, measureValues));
+    }
+
+    // Apply the unpivot operation
+    context.relBuilder.unpivot(
+        false, // includeNulls = false
+        measureColumns, // measure column names: ["value"]
+        axisColumns, // axis column names: ["column"]
+        valueMappings // field mappings
+        );
+
+    // Pivot the data to transpose rows as columns
+    // Pivot on __row_id__ with column as the grouping key
+    // This creates: column, row1, row2, row3, ...
+
+    // Create conditional aggregations for each row position
+    // We'll use ROW_NUMBER to determine the row positions dynamically
+    RexNode rowPos =
+        context
+            .relBuilder
+            .aggregateCall(SqlStdOperatorTable.ROW_NUMBER)
+            .over()
+            .partitionBy(context.relBuilder.field(columnName))
+            .orderBy(context.relBuilder.field("__row_id__"))
+            .rowsTo(RexWindowBounds.CURRENT_ROW)
+            .as("__row_pos__");
+    context.relBuilder.projectPlus(rowPos);
+
+    // Create aggregation calls for each possible row position
+    List<AggCall> pivotAggCalls = new ArrayList<>();
+
+    for (int i = 1; i <= maxRows; i++) {
+      // Create CASE WHEN __row_id__ = i THEN value END for each row position
+      RexNode caseExpr =
+          context.relBuilder.call(
+              SqlStdOperatorTable.CASE,
+              context.relBuilder.equals(
+                  context.relBuilder.field("__row_id__"), context.relBuilder.literal(i)),
+              context.relBuilder.field("value"),
+              context.relBuilder.literal(null));
+
+      AggCall maxCase = context.relBuilder.max(caseExpr).as("row " + i);
+      pivotAggCalls.add(maxCase);
+    }
+
+    // Group by column and apply the conditional aggregations
+    context.relBuilder.aggregate(
+        context.relBuilder.groupKey(context.relBuilder.field(columnName)), pivotAggCalls);
+
+    return context.relBuilder.peek();
+  }
+
   @Override
   public RelNode visitBin(Bin node, CalcitePlanContext context) {
     visitChildren(node, context);

docs/category.json

@@ -43,6 +43,7 @@
     "user/ppl/cmd/timechart.md",
     "user/ppl/cmd/top.md",
     "user/ppl/cmd/trendline.md",
+    "user/ppl/cmd/transpose.md",
     "user/ppl/cmd/where.md",
     "user/ppl/functions/aggregations.md",
     "user/ppl/functions/collection.md",

docs/user/ppl/cmd/transpose.md

@@ -0,0 +1,92 @@
+# transpose  
+
+## Description  
+
+The `transpose` command outputs the requested number of rows as columns, effectively transposing each result row into a corresponding column of field values.
+
+## Syntax  
+
+transpose [int] [column_name=<string>]
+
+* number-of-rows: optional. The number of rows to transform into columns.  
+* column_name: optional. The name of the first column to use when transposing rows. This column holds the field names.  
+
+
+## Example 1: Transpose results   
+
+This example shows transposing wihtout any parameters. It transforms 5 rows into columns as default is 5.
+
+```ppl
+source=accounts
+| head 5 
+| fields account_number, firstname,  lastname, balance 
+| transpose
+```
+
+Expected output:
+
+```text
+fetched rows / total rows = 4/4
++----------------+-------+--------+---------+-------+-------+
+| column         | row 1 | row 2  | row 3   | row 4 | row 5 |
+|----------------+-------+--------+---------+-------+-------|
+| account_number | 1     | 6      | 13      | 18    | null  |
+| firstname      | Amber | Hattie | Nanette | Dale  | null  |
+| balance        | 39225 | 5686   | 32838   | 4180  | null  |
+| lastname       | Duke  | Bond   | Bates   | Adams | null  |
++----------------+-------+--------+---------+-------+-------+
+```
+
+## Example 2: Tranpose results up to a provided number of rows.  
+
+This example shows transposing wihtout any parameters. It transforms 4 rows into columns as default is 5.
+
+```ppl
+source=accounts
+| head 5 
+| fields  account_number, firstname,  lastname, balance 
+| transpose 4
+```
+
+Expected output:
+
+```text
+fetched rows / total rows = 4/4
++----------------+-------+--------+---------+-------+
+| column         | row 1 | row 2  | row 3   | row 4 |
+|----------------+-------+--------+---------+-------|
+| account_number | 1     | 6      | 13      | 18    |
+| firstname      | Amber | Hattie | Nanette | Dale  |
+| balance        | 39225 | 5686   | 32838   | 4180  |
+| lastname       | Duke  | Bond   | Bates   | Adams |
++----------------+-------+--------+---------+-------+
+```
+
+## Example 2: Tranpose results up to a provided number of rows and first column with specified column name.
+
+This example shows transposing wihtout any parameters. It transforms 4 rows into columns as default is 5.
+
+```ppl
+source=accounts
+| head 5 
+| fields  account_number, firstname,  lastname, balance 
+| transpose 4 column_name='column_names'
+```
+
+Expected output:
+
+```text
+fetched rows / total rows = 4/4
++----------------+-------+--------+---------+-------+
+| column_names   | row 1 | row 2  | row 3   | row 4 |
+|----------------+-------+--------+---------+-------|
+| account_number | 1     | 6      | 13      | 18    |
+| firstname      | Amber | Hattie | Nanette | Dale  |
+| balance        | 39225 | 5686   | 32838   | 4180  |
+| lastname       | Duke  | Bond   | Bates   | Adams |
++----------------+-------+--------+---------+-------+
+```
+
+## Limitations  
+
+The `transpose` command transforms up to a number of rows specified and if not enough rows found, it shows those transposed rows as null columns.