Add mvappend function for Calcite PPL

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

@@ -62,6 +62,7 @@ public enum BuiltinFunctionName {
   /** Collection functions */
   ARRAY(FunctionName.of("array")),
   ARRAY_LENGTH(FunctionName.of("array_length")),
+  MVAPPEND(FunctionName.of("mvappend")),
   MVJOIN(FunctionName.of("mvjoin")),
   FORALL(FunctionName.of("forall")),
   EXISTS(FunctionName.of("exists")),

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

@@ -0,0 +1,130 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.expression.function.CollectionUDF;
+
+import static org.apache.calcite.sql.type.SqlTypeUtil.createArrayType;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.apache.calcite.adapter.enumerable.NotNullImplementor;
+import org.apache.calcite.adapter.enumerable.NullPolicy;
+import org.apache.calcite.adapter.enumerable.RexToLixTranslator;
+import org.apache.calcite.linq4j.tree.Expression;
+import org.apache.calcite.linq4j.tree.Expressions;
+import org.apache.calcite.linq4j.tree.Types;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rel.type.RelDataTypeFactory;
+import org.apache.calcite.rex.RexCall;
+import org.apache.calcite.sql.SqlOperatorBinding;
+import org.apache.calcite.sql.type.SqlReturnTypeInference;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.opensearch.sql.expression.function.ImplementorUDF;
+import org.opensearch.sql.expression.function.UDFOperandMetadata;
+
+/**
+ * MVAppend function that appends all elements from arguments to create an array. Always returns an
+ * array or null for consistent type behavior.
+ */
+public class MVAppendFunctionImpl extends ImplementorUDF {
+
+  public MVAppendFunctionImpl() {
+    super(new MVAppendImplementor(), NullPolicy.ALL);
+  }
+
+  @Override
+  public SqlReturnTypeInference getReturnTypeInference() {
+    return sqlOperatorBinding -> {
+      RelDataTypeFactory typeFactory = sqlOperatorBinding.getTypeFactory();
+
+      if (sqlOperatorBinding.getOperandCount() == 0) {
+        return typeFactory.createSqlType(SqlTypeName.NULL);
+      }
+
+      RelDataType elementType = determineElementType(sqlOperatorBinding, typeFactory);
+      return createArrayType(
+          typeFactory, typeFactory.createTypeWithNullability(elementType, true), true);
+    };
+  }
+
+  @Override
+  public UDFOperandMetadata getOperandMetadata() {
+    return null;
+  }
+
+  private static RelDataType determineElementType(
+      SqlOperatorBinding sqlOperatorBinding, RelDataTypeFactory typeFactory) {
+    RelDataType mostGeneralType = null;
+
+    for (int i = 0; i < sqlOperatorBinding.getOperandCount(); i++) {
+      RelDataType operandType = getComponentType(sqlOperatorBinding.getOperandType(i));
+
+      mostGeneralType = updateMostGeneralType(mostGeneralType, operandType, typeFactory);
+    }
+
+    return mostGeneralType != null ? mostGeneralType : typeFactory.createSqlType(SqlTypeName.NULL);
+  }
+
+  private static RelDataType getComponentType(RelDataType operandType) {
+    if (!operandType.isStruct() && operandType.getComponentType() != null) {
+      return operandType.getComponentType();
+    }
+    return operandType;
+  }
+
+  private static RelDataType updateMostGeneralType(
+      RelDataType current, RelDataType candidate, RelDataTypeFactory typeFactory) {
+    if (current == null) {
+      return candidate;
+    }
+
+    if (!current.equals(candidate)) {
+      return typeFactory.createSqlType(SqlTypeName.ANY);
+    } else {
+      return current;
+    }
+  }
+
+  public static class MVAppendImplementor implements NotNullImplementor {
+    @Override
+    public Expression implement(
+        RexToLixTranslator translator, RexCall call, List<Expression> translatedOperands) {
+      return Expressions.call(
+          Types.lookupMethod(MVAppendFunctionImpl.class, "mvappend", Object[].class),
+          Expressions.newArrayInit(Object.class, translatedOperands));
+    }
+  }
+
+  public static Object mvappend(Object... args) {
+    List<Object> elements = collectElements(args);
+    return elements.isEmpty() ? null : elements;
+  }
+
+  private static List<Object> collectElements(Object... args) {
+    List<Object> elements = new ArrayList<>();
+
+    for (Object arg : args) {
+      if (arg == null) {
+        continue;
+      }
+
+      if (arg instanceof List) {
+        addListElements((List<?>) arg, elements);
+      } else {
+        elements.add(arg);
+      }
+    }
+
+    return elements;
+  }
+
+  private static void addListElements(List<?> list, List<Object> elements) {
+    for (Object item : list) {
+      if (item != null) {
+        elements.add(item);
+      }
+    }
+  }
+}

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

@@ -46,6 +46,7 @@
 import org.opensearch.sql.expression.function.CollectionUDF.ExistsFunctionImpl;
 import org.opensearch.sql.expression.function.CollectionUDF.FilterFunctionImpl;
 import org.opensearch.sql.expression.function.CollectionUDF.ForallFunctionImpl;
+import org.opensearch.sql.expression.function.CollectionUDF.MVAppendFunctionImpl;
 import org.opensearch.sql.expression.function.CollectionUDF.ReduceFunctionImpl;
 import org.opensearch.sql.expression.function.CollectionUDF.TransformFunctionImpl;
 import org.opensearch.sql.expression.function.jsonUDF.JsonAppendFunctionImpl;
@@ -383,6 +384,7 @@ public class PPLBuiltinOperators extends ReflectiveSqlOperatorTable {
   public static final SqlOperator FORALL = new ForallFunctionImpl().toUDF("forall");
   public static final SqlOperator EXISTS = new ExistsFunctionImpl().toUDF("exists");
   public static final SqlOperator ARRAY = new ArrayFunctionImpl().toUDF("array");
+  public static final SqlOperator MVAPPEND = new MVAppendFunctionImpl().toUDF("mvappend");
   public static final SqlOperator FILTER = new FilterFunctionImpl().toUDF("filter");
   public static final SqlOperator TRANSFORM = new TransformFunctionImpl().toUDF("transform");
   public static final SqlOperator REDUCE = new ReduceFunctionImpl().toUDF("reduce");

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

@@ -144,6 +144,7 @@
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.MULTIPLY;
 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.MVJOIN;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.NOT;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.NOTEQUAL;
@@ -834,6 +835,7 @@ void populate() {
           PPLTypeChecker.family(SqlTypeFamily.ARRAY, SqlTypeFamily.CHARACTER));
 
       registerOperator(ARRAY, PPLBuiltinOperators.ARRAY);
+      registerOperator(MVAPPEND, PPLBuiltinOperators.MVAPPEND);
       registerOperator(ARRAY_LENGTH, SqlLibraryOperators.ARRAY_LENGTH);
       registerOperator(FORALL, PPLBuiltinOperators.FORALL);
       registerOperator(EXISTS, PPLBuiltinOperators.EXISTS);

core/src/test/java/org/opensearch/sql/expression/function/CollectionUDF/MVAppendFunctionImplTest.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.expression.function.CollectionUDF;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import java.util.Arrays;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+/** Unit tests for MVAppendFunctionImpl. */
+public class MVAppendFunctionImplTest {
+
+  @Test
+  public void testMvappendWithNoArguments() {
+    Object result = MVAppendFunctionImpl.mvappend();
+    assertNull(result);
+  }
+
+  @Test
+  public void testMvappendWithSingleElement() {
+    Object result = MVAppendFunctionImpl.mvappend(42);
+    assertEquals(Arrays.asList(42), result);
+  }
+
+  @Test
+  public void testMvappendWithMultipleElements() {
+    Object result = MVAppendFunctionImpl.mvappend(1, 2, 3);
+    assertEquals(Arrays.asList(1, 2, 3), result);
+  }
+
+  @Test
+  public void testMvappendWithNullValues() {
+    Object result = MVAppendFunctionImpl.mvappend(null, 1, null);
+    assertEquals(Arrays.asList(1), result);
+  }
+
+  @Test
+  public void testMvappendWithAllNulls() {
+    Object result = MVAppendFunctionImpl.mvappend(null, null);
+    assertNull(result);
+  }
+
+  @Test
+  public void testMvappendWithArrayFlattening() {
+    List<Integer> array1 = Arrays.asList(1, 2);
+    List<Integer> array2 = Arrays.asList(3, 4);
+    Object result = MVAppendFunctionImpl.mvappend(array1, array2);
+    assertEquals(Arrays.asList(1, 2, 3, 4), result);
+  }
+
+  @Test
+  public void testMvappendWithMixedTypes() {
+    List<Integer> array = Arrays.asList(1, 2);
+    Object result = MVAppendFunctionImpl.mvappend(array, 3, "hello");
+    assertEquals(Arrays.asList(1, 2, 3, "hello"), result);
+  }
+
+  @Test
+  public void testMvappendWithArrayAndNulls() {
+    List<Integer> array = Arrays.asList(1, 2);
+    Object result = MVAppendFunctionImpl.mvappend(null, array, null, 3);
+    assertEquals(Arrays.asList(1, 2, 3), result);
+  }
+
+  @Test
+  public void testMvappendWithSingleNull() {
+    Object result = MVAppendFunctionImpl.mvappend((Object) null);
+    assertNull(result);
+  }
+
+  @Test
+  public void testMvappendWithEmptyArray() {
+    List<Object> emptyArray = Arrays.asList();
+    Object result = MVAppendFunctionImpl.mvappend(emptyArray, 1);
+    assertEquals(Arrays.asList(1), result);
+  }
+}

docs/category.json

@@ -54,6 +54,7 @@
     "user/ppl/cmd/top.rst",
     "user/ppl/cmd/trendline.rst",
     "user/ppl/cmd/where.rst",
+    "user/ppl/functions/collection.rst",
     "user/ppl/functions/condition.rst",
     "user/ppl/functions/datetime.rst",
     "user/ppl/functions/expressions.rst",