Support mvindex eval function

core/src/main/java/org/opensearch/sql/expression/function/BuiltinFunctionName.java

@@ -68,11 +68,13 @@ public enum BuiltinFunctionName {
   /** Collection functions */
   ARRAY(FunctionName.of("array")),
   ARRAY_LENGTH(FunctionName.of("array_length")),
+  ARRAY_SLICE(FunctionName.of("array_slice"), true),
   MAP_APPEND(FunctionName.of("map_append"), true),
   MAP_CONCAT(FunctionName.of("map_concat"), true),
   MAP_REMOVE(FunctionName.of("map_remove"), true),
   MVAPPEND(FunctionName.of("mvappend")),
   MVJOIN(FunctionName.of("mvjoin")),
+  MVINDEX(FunctionName.of("mvindex")),
   FORALL(FunctionName.of("forall")),
   EXISTS(FunctionName.of("exists")),
   FILTER(FunctionName.of("filter")),

core/src/main/java/org/opensearch/sql/expression/function/CollectionUDF/MVIndexFunctionImp.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.expression.function.CollectionUDF;
+
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.ADDFUNCTION;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.ARRAY_LENGTH;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.ARRAY_SLICE;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.IF;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.INTERNAL_ITEM;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.LESS;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.SUBTRACT;
+
+import java.math.BigDecimal;
+import org.apache.calcite.rex.RexBuilder;
+import org.apache.calcite.rex.RexNode;
+import org.opensearch.sql.expression.function.PPLFuncImpTable;
+
+/**
+ * MVINDEX function implementation that returns a subset of a multivalue array.
+ *
+ * <p>Usage:
+ *
+ * <ul>
+ *   <li>mvindex(array, start) - returns single element at index (0-based)
+ *   <li>mvindex(array, start, end) - returns array slice from start to end (inclusive, 0-based)
+ * </ul>
+ *
+ * <p>Supports negative indexing where -1 refers to the last element.
+ *
+ * <p>Implementation notes:
+ *
+ * <ul>
+ *   <li>Single element access uses Calcite's ITEM operator (1-based indexing)
+ *   <li>Range access uses Calcite's ARRAY_SLICE operator (0-based indexing with length parameter)
+ *   <li>Index conversion handles the difference between PPL's 0-based indexing and Calcite's
+ *       conventions
+ * </ul>
+ */
+public class MVIndexFunctionImp implements PPLFuncImpTable.FunctionImp {
+
+  @Override
+  public RexNode resolve(RexBuilder builder, RexNode... args) {
+    RexNode array = args[0];
+    RexNode startIdx = args[1];
+
+    // Use resolve to get array length instead of direct makeCall
+    RexNode arrayLen = PPLFuncImpTable.INSTANCE.resolve(builder, ARRAY_LENGTH, array);
+
+    if (args.length == 2) {
+      // Single element access using ITEM (1-based indexing)
+      return resolveSingleElement(builder, array, startIdx, arrayLen);
+    } else {
+      // Range access using ARRAY_SLICE (0-based indexing)
+      RexNode endIdx = args[2];
+      return resolveRange(builder, array, startIdx, endIdx, arrayLen);
+    }
+  }
+
+  /**
+   * Resolves single element access: mvindex(array, index)
+   *
+   * <p>Uses Calcite's ITEM operator which uses 1-based indexing. Converts PPL's 0-based index to
+   * 1-based by adding 1.
+   */
+  private RexNode resolveSingleElement(
+      RexBuilder builder, RexNode array, RexNode startIdx, RexNode arrayLen) {
+    // Convert 0-based PPL index to 1-based Calcite ITEM index
+    RexNode zero = builder.makeExactLiteral(BigDecimal.ZERO);
+    RexNode one = builder.makeExactLiteral(BigDecimal.ONE);
+
+    RexNode isNegative = PPLFuncImpTable.INSTANCE.resolve(builder, LESS, startIdx, zero);
+    RexNode sumArrayLenStart =
+        PPLFuncImpTable.INSTANCE.resolve(builder, ADDFUNCTION, arrayLen, startIdx);
+    RexNode negativeCase =
+        PPLFuncImpTable.INSTANCE.resolve(builder, ADDFUNCTION, sumArrayLenStart, one);
+    RexNode positiveCase = PPLFuncImpTable.INSTANCE.resolve(builder, ADDFUNCTION, startIdx, one);
+
+    RexNode normalizedStart =
+        PPLFuncImpTable.INSTANCE.resolve(builder, IF, isNegative, negativeCase, positiveCase);
+
+    return PPLFuncImpTable.INSTANCE.resolve(builder, INTERNAL_ITEM, array, normalizedStart);
+  }
+
+  /**
+   * Resolves range access: mvindex(array, start, end)
+   *
+   * <p>Uses Calcite's ARRAY_SLICE operator which uses 0-based indexing and a length parameter.
+   * PPL's end index is inclusive, so length = (end - start) + 1.
+   */
+  private RexNode resolveRange(
+      RexBuilder builder, RexNode array, RexNode startIdx, RexNode endIdx, RexNode arrayLen) {
+    // Normalize negative indices for ARRAY_SLICE (0-based)
+    RexNode zero = builder.makeExactLiteral(BigDecimal.ZERO);
+    RexNode one = builder.makeExactLiteral(BigDecimal.ONE);
+
+    RexNode isStartNegative = PPLFuncImpTable.INSTANCE.resolve(builder, LESS, startIdx, zero);
+    RexNode startNegativeCase =
+        PPLFuncImpTable.INSTANCE.resolve(builder, ADDFUNCTION, arrayLen, startIdx);
+    RexNode normalizedStart =
+        PPLFuncImpTable.INSTANCE.resolve(builder, IF, isStartNegative, startNegativeCase, startIdx);
+
+    RexNode isEndNegative = PPLFuncImpTable.INSTANCE.resolve(builder, LESS, endIdx, zero);
+    RexNode endNegativeCase =
+        PPLFuncImpTable.INSTANCE.resolve(builder, ADDFUNCTION, arrayLen, endIdx);
+    RexNode normalizedEnd =
+        PPLFuncImpTable.INSTANCE.resolve(builder, IF, isEndNegative, endNegativeCase, endIdx);
+
+    // Calculate length: (normalizedEnd - normalizedStart) + 1
+    RexNode diff =
+        PPLFuncImpTable.INSTANCE.resolve(builder, SUBTRACT, normalizedEnd, normalizedStart);
+    RexNode length = PPLFuncImpTable.INSTANCE.resolve(builder, ADDFUNCTION, diff, one);
+
+    // Call ARRAY_SLICE(array, normalizedStart, length)
+    return PPLFuncImpTable.INSTANCE.resolve(builder, ARRAY_SLICE, array, normalizedStart, length);
+  }
+}

core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java

@@ -17,6 +17,7 @@
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.AND;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.ARRAY;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.ARRAY_LENGTH;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.ARRAY_SLICE;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.ASCII;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.ASIN;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.ATAN;
@@ -150,6 +151,7 @@
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.MULTIPLYFUNCTION;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.MULTI_MATCH;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.MVAPPEND;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.MVINDEX;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.MVJOIN;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.NOT;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.NOTEQUAL;
@@ -283,6 +285,7 @@
 import org.opensearch.sql.calcite.utils.UserDefinedFunctionUtils;
 import org.opensearch.sql.exception.ExpressionEvaluationException;
 import org.opensearch.sql.executor.QueryType;
+import org.opensearch.sql.expression.function.CollectionUDF.MVIndexFunctionImp;
 
 public class PPLFuncImpTable {
   private static final Logger logger = LogManager.getLogger(PPLFuncImpTable.class);
@@ -974,12 +977,25 @@ void populate() {
                   builder.makeCall(SqlLibraryOperators.ARRAY_JOIN, array, delimiter),
           PPLTypeChecker.family(SqlTypeFamily.ARRAY, SqlTypeFamily.CHARACTER));
 
+      // Register MVINDEX to use Calcite's ITEM/ARRAY_SLICE with index normalization
+      register(
+          MVINDEX,
+          new MVIndexFunctionImp(),
+          PPLTypeChecker.wrapComposite(
+              (CompositeOperandTypeChecker)
+                  OperandTypes.family(SqlTypeFamily.ARRAY, SqlTypeFamily.INTEGER)
+                      .or(
+                          OperandTypes.family(
+                              SqlTypeFamily.ARRAY, SqlTypeFamily.INTEGER, SqlTypeFamily.INTEGER)),
+              false));
+
       registerOperator(ARRAY, PPLBuiltinOperators.ARRAY);
       registerOperator(MVAPPEND, PPLBuiltinOperators.MVAPPEND);
       registerOperator(MAP_APPEND, PPLBuiltinOperators.MAP_APPEND);
       registerOperator(MAP_CONCAT, SqlLibraryOperators.MAP_CONCAT);
       registerOperator(MAP_REMOVE, PPLBuiltinOperators.MAP_REMOVE);
       registerOperator(ARRAY_LENGTH, SqlLibraryOperators.ARRAY_LENGTH);
+      registerOperator(ARRAY_SLICE, SqlLibraryOperators.ARRAY_SLICE);
       registerOperator(FORALL, PPLBuiltinOperators.FORALL);
       registerOperator(EXISTS, PPLBuiltinOperators.EXISTS);
       registerOperator(FILTER, PPLBuiltinOperators.FILTER);

docs/user/ppl/functions/collection.rst

@@ -301,3 +301,58 @@ Example::
     |--------------|
     | [1,text,2.5] |
     +--------------+
+
+MVINDEX
+-------
+
+Description
+>>>>>>>>>>>
+
+Usage: mvindex(array, start, [end]) returns a subset of the multivalue array using the start and optional end index values. Indexes are 0-based (first element is at index 0). Supports negative indexing where -1 refers to the last element. When only start is provided, returns a single element. When both start and end are provided, returns an array of elements from start to end (inclusive).
+
+Argument type: array: ARRAY, start: INTEGER, end: INTEGER (optional)
+
+Return type: ANY (single element) or ARRAY (range)
+
+Example::
+
+    os> source=people | eval array = array('a', 'b', 'c', 'd', 'e'), result = mvindex(array, 1) | fields result | head 1
+    fetched rows / total rows = 1/1
+    +--------+
+    | result |
+    |--------|
+    | b      |
+    +--------+
+
+    os> source=people | eval array = array('a', 'b', 'c', 'd', 'e'), result = mvindex(array, -1) | fields result | head 1
+    fetched rows / total rows = 1/1
+    +--------+
+    | result |
+    |--------|
+    | e      |
+    +--------+
+
+    os> source=people | eval array = array(1, 2, 3, 4, 5), result = mvindex(array, 1, 3) | fields result | head 1
+    fetched rows / total rows = 1/1
+    +---------+
+    | result  |
+    |---------|
+    | [2,3,4] |
+    +---------+
+
+    os> source=people | eval array = array(1, 2, 3, 4, 5), result = mvindex(array, -3, -1) | fields result | head 1
+    fetched rows / total rows = 1/1
+    +---------+
+    | result  |
+    |---------|
+    | [3,4,5] |
+    +---------+
+
+    os> source=people | eval array = array('alex', 'celestino', 'claudia', 'david'), result = mvindex(array, 0, 2) | fields result | head 1
+    fetched rows / total rows = 1/1
+    +--------------------------+
+    | result                   |
+    |--------------------------|
+    | [alex,celestino,claudia] |
+    +--------------------------+
+

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalciteArrayFunctionIT.java

@@ -370,4 +370,123 @@ public void testMvjoinWithMultipleRealFields() throws IOException {
         firstRow.getString(0) + " | " + firstRow.getString(1) + " | " + firstRow.getString(2),
         firstRow.getString(3));
   }
+
+  @Test
+  public void testMvindexSingleElementPositive() throws IOException {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | eval arr = array('a', 'b', 'c', 'd', 'e'), result = mvindex(arr, 1)"
+                    + " | head 1 | fields result",
+                TEST_INDEX_BANK));
+
+    verifySchema(actual, schema("result", "string"));
+    verifyDataRows(actual, rows("b"));
+  }
+
+  @Test
+  public void testMvindexSingleElementNegative() throws IOException {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | eval arr = array('a', 'b', 'c', 'd', 'e'), result = mvindex(arr, -1)"
+                    + " | head 1 | fields result",
+                TEST_INDEX_BANK));
+
+    verifySchema(actual, schema("result", "string"));
+    verifyDataRows(actual, rows("e"));
+  }
+
+  @Test
+  public void testMvindexSingleElementNegativeMiddle() throws IOException {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | eval arr = array('a', 'b', 'c', 'd', 'e'), result = mvindex(arr, -3)"
+                    + " | head 1 | fields result",
+                TEST_INDEX_BANK));
+
+    verifySchema(actual, schema("result", "string"));
+    verifyDataRows(actual, rows("c"));
+  }
+
+  @Test
+  public void testMvindexRangePositive() throws IOException {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | eval arr = array(1, 2, 3, 4, 5), result = mvindex(arr, 1, 3) | head"
+                    + " 1 | fields result",
+                TEST_INDEX_BANK));
+
+    verifySchema(actual, schema("result", "array"));
+    verifyDataRows(actual, rows(List.of(2, 3, 4)));
+  }
+
+  @Test
+  public void testMvindexRangeNegative() throws IOException {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | eval arr = array(1, 2, 3, 4, 5), result = mvindex(arr, -3, -1) |"
+                    + " head 1 | fields result",
+                TEST_INDEX_BANK));
+
+    verifySchema(actual, schema("result", "array"));
+    verifyDataRows(actual, rows(List.of(3, 4, 5)));
+  }
+
+  @Test
+  public void testMvindexRangeMixed() throws IOException {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | eval arr = array(1, 2, 3, 4, 5), result = mvindex(arr, -4, 2) | head"
+                    + " 1 | fields result",
+                TEST_INDEX_BANK));
+
+    verifySchema(actual, schema("result", "array"));
+    verifyDataRows(actual, rows(List.of(2, 3)));
+  }
+
+  @Test
+  public void testMvindexRangeFirstThree() throws IOException {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | eval arr = array('alex', 'celestino', 'claudia', 'david'), result ="
+                    + " mvindex(arr, 0, 2) | head 1 | fields result",
+                TEST_INDEX_BANK));
+
+    verifySchema(actual, schema("result", "array"));
+    verifyDataRows(actual, rows(List.of("alex", "celestino", "claudia")));
+  }
+
+  @Test
+  public void testMvindexRangeLastThree() throws IOException {
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | eval arr = array('buttercup', 'dash', 'flutter', 'honey', 'ivory',"
+                    + " 'minty', 'pinky', 'rarity'), result = mvindex(arr, -3, -1) | head 1 |"
+                    + " fields result",
+                TEST_INDEX_BANK));
+
+    verifySchema(actual, schema("result", "array"));
+    verifyDataRows(actual, rows(List.of("minty", "pinky", "rarity")));
+  }
+
+  @Test
+  public void testMvindexRangeSingleElement() throws IOException {
+    // When start == end, should return single element in array
+    JSONObject actual =
+        executeQuery(
+            String.format(
+                "source=%s | eval arr = array(1, 2, 3, 4, 5), result = mvindex(arr, 2, 2) | head"
+                    + " 1 | fields result",
+                TEST_INDEX_BANK));
+
+    verifySchema(actual, schema("result", "array"));
+    verifyDataRows(actual, rows(List.of(3)));
+  }
 }

ppl/src/main/antlr/OpenSearchPPLLexer.g4

@@ -439,6 +439,7 @@ ARRAY:                              'ARRAY';
 ARRAY_LENGTH:                       'ARRAY_LENGTH';
 MVAPPEND:                           'MVAPPEND';
 MVJOIN:                             'MVJOIN';
+MVINDEX:                            'MVINDEX';
 FORALL:                             'FORALL';
 FILTER:                             'FILTER';
 TRANSFORM:                          'TRANSFORM';

ppl/src/main/antlr/OpenSearchPPLParser.g4

@@ -1081,6 +1081,7 @@ collectionFunctionName
     | ARRAY_LENGTH
     | MVAPPEND
     | MVJOIN
+    | MVINDEX
     | FORALL
     | EXISTS
     | FILTER