[Backport 2.x] Add Nested Support in Select Clause (#1490)

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

@@ -366,6 +366,14 @@ public LogicalPlan visitProject(Project node, AnalysisContext context) {
     List<NamedExpression> namedExpressions =
         selectExpressionAnalyzer.analyze(node.getProjectList(), context,
             new ExpressionReferenceOptimizer(expressionAnalyzer.getRepository(), child));
+
+    for (UnresolvedExpression expr : node.getProjectList()) {
+      NestedAnalyzer nestedAnalyzer = new NestedAnalyzer(
+          namedExpressions, expressionAnalyzer, child
+      );
+      child = nestedAnalyzer.analyze(expr, context);
+    }
+
     // new context
     context.push();
     TypeEnvironment newEnv = context.peek();

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

@@ -416,17 +416,6 @@ private Expression visitIdentifier(String ident, AnalysisContext context) {
     ReferenceExpression ref = DSL.ref(ident,
         typeEnv.resolve(new Symbol(Namespace.FIELD_NAME, ident)));
 
-    // Fall back to old engine too if type is not supported semantically
-    if (isTypeNotSupported(ref.type())) {
-      throw new SyntaxCheckException(String.format(
-          "Identifier [%s] of type [%s] is not supported yet", ident, ref.type()));
-    }
     return ref;
   }
-
-  // Array type is not supporte yet.
-  private boolean isTypeNotSupported(ExprType type) {
-    return "array".equalsIgnoreCase(type.typeName());
-  }
-
 }

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

@@ -0,0 +1,111 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.analysis;
+
+import static org.opensearch.sql.data.type.ExprCoreType.STRING;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import lombok.RequiredArgsConstructor;
+import org.opensearch.sql.ast.AbstractNodeVisitor;
+import org.opensearch.sql.ast.expression.Alias;
+import org.opensearch.sql.ast.expression.Function;
+import org.opensearch.sql.ast.expression.QualifiedName;
+import org.opensearch.sql.ast.expression.UnresolvedExpression;
+import org.opensearch.sql.expression.NamedExpression;
+import org.opensearch.sql.expression.ReferenceExpression;
+import org.opensearch.sql.expression.function.BuiltinFunctionName;
+import org.opensearch.sql.planner.logical.LogicalNested;
+import org.opensearch.sql.planner.logical.LogicalPlan;
+
+/**
+ * Analyze the Nested Function in the {@link AnalysisContext} to construct the {@link
+ * LogicalPlan}.
+ */
+@RequiredArgsConstructor
+public class NestedAnalyzer extends AbstractNodeVisitor<LogicalPlan, AnalysisContext> {
+  private final List<NamedExpression> namedExpressions;
+  private final ExpressionAnalyzer expressionAnalyzer;
+  private final LogicalPlan child;
+
+  public LogicalPlan analyze(UnresolvedExpression projectItem, AnalysisContext context) {
+    LogicalPlan nested = projectItem.accept(this, context);
+    return (nested == null) ? child : nested;
+  }
+
+  @Override
+  public LogicalPlan visitAlias(Alias node, AnalysisContext context) {
+    return node.getDelegated().accept(this, context);
+  }
+
+  @Override
+  public LogicalPlan visitFunction(Function node, AnalysisContext context) {
+    if (node.getFuncName().equalsIgnoreCase(BuiltinFunctionName.NESTED.name())) {
+
+      List<UnresolvedExpression> expressions = node.getFuncArgs();
+      validateArgs(expressions);
+      ReferenceExpression nestedField =
+          (ReferenceExpression)expressionAnalyzer.analyze(expressions.get(0), context);
+      Map<String, ReferenceExpression> args;
+      if (expressions.size() == 2) {
+        args = Map.of(
+            "field", nestedField,
+            "path", (ReferenceExpression)expressionAnalyzer.analyze(expressions.get(1), context)
+        );
+      } else {
+        args = Map.of(
+            "field", (ReferenceExpression)expressionAnalyzer.analyze(expressions.get(0), context),
+            "path", generatePath(nestedField.toString())
+        );
+      }
+      if (child instanceof LogicalNested) {
+        ((LogicalNested)child).addFields(args);
+        return child;
+      } else {
+        return new LogicalNested(child, new ArrayList<>(Arrays.asList(args)), namedExpressions);
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Validate each parameter used in nested function in SELECT clause. Any supplied parameter
+   * for a nested function in a SELECT statement must be a valid qualified name, and the field
+   * parameter must be nested at least one level.
+   * @param args : Arguments in nested function.
+   */
+  private void validateArgs(List<UnresolvedExpression> args) {
+    if (args.size() < 1 || args.size() > 2) {
+      throw new IllegalArgumentException(
+          "on nested object only allowed 2 parameters (field,path) or 1 parameter (field)"
+      );
+    }
+
+    for (int i = 0; i < args.size(); i++) {
+      if (!(args.get(i) instanceof QualifiedName)) {
+        throw new IllegalArgumentException(
+            String.format("Illegal nested field name: %s", args.get(i).toString())
+        );
+      }
+      if (i == 0 && ((QualifiedName)args.get(i)).getParts().size() < 2) {
+        throw new IllegalArgumentException(
+            String.format("Illegal nested field name: %s", args.get(i).toString())
+        );
+      }
+    }
+  }
+
+  /**
+   * Generate nested path dynamically. Assumes at least one level of nesting in supplied string.
+   * @param field : Nested field to generate path of.
+   * @return : Path of field derived from last level of nesting.
+   */
+  private ReferenceExpression generatePath(String field) {
+    return new ReferenceExpression(field.substring(0, field.lastIndexOf(".")), STRING);
+  }
+}

core/src/main/java/org/opensearch/sql/executor/Explain.java

@@ -23,6 +23,7 @@
 import org.opensearch.sql.planner.physical.EvalOperator;
 import org.opensearch.sql.planner.physical.FilterOperator;
 import org.opensearch.sql.planner.physical.LimitOperator;
+import org.opensearch.sql.planner.physical.NestedOperator;
 import org.opensearch.sql.planner.physical.PhysicalPlan;
 import org.opensearch.sql.planner.physical.PhysicalPlanNodeVisitor;
 import org.opensearch.sql.planner.physical.ProjectOperator;
@@ -142,6 +143,12 @@ public ExplainResponseNode visitLimit(LimitOperator node, Object context) {
         "limit", node.getLimit(), "offset", node.getOffset())));
   }
 
+  @Override
+  public ExplainResponseNode visitNested(NestedOperator node, Object context) {
+    return explain(node, context, explanNode -> explanNode.setDescription(ImmutableMap.of(
+        "nested", node.getFields())));
+  }
+
   protected ExplainResponseNode explain(PhysicalPlan node, Object context,
                                         Consumer<ExplainResponseNode> doExplain) {
     ExplainResponseNode explainNode = new ExplainResponseNode(getOperatorName(node));

core/src/main/java/org/opensearch/sql/expression/DSL.java

@@ -620,6 +620,10 @@ public static FunctionExpression xor(Expression... expressions) {
     return compile(FunctionProperties.None, BuiltinFunctionName.XOR, expressions);
   }
 
+  public static FunctionExpression nested(Expression... expressions) {
+    return compile(FunctionProperties.None, BuiltinFunctionName.NESTED, expressions);
+  }
+
   public static FunctionExpression not(Expression... expressions) {
     return compile(FunctionProperties.None, BuiltinFunctionName.NOT, expressions);
   }

core/src/main/java/org/opensearch/sql/expression/ReferenceExpression.java

@@ -15,6 +15,7 @@
 import lombok.RequiredArgsConstructor;
 import org.opensearch.sql.data.model.ExprTupleValue;
 import org.opensearch.sql.data.model.ExprValue;
+import org.opensearch.sql.data.type.ExprCoreType;
 import org.opensearch.sql.data.type.ExprType;
 import org.opensearch.sql.expression.env.Environment;
 
@@ -100,7 +101,12 @@ public ExprValue resolve(ExprTupleValue value) {
   }
 
   private ExprValue resolve(ExprValue value, List<String> paths) {
-    final ExprValue wholePathValue = value.keyValue(String.join(PATH_SEP, paths));
+    ExprValue wholePathValue = value.keyValue(String.join(PATH_SEP, paths));
+    // For array types only first index currently supported.
+    if (value.type().equals(ExprCoreType.ARRAY)) {
+      wholePathValue = value.collectionValue().get(0).keyValue(paths.get(0));
+    }
+
     if (!wholePathValue.isMissing() || paths.size() == 1) {
       return wholePathValue;
     } else {

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

@@ -188,6 +188,8 @@ public enum BuiltinFunctionName {
   STDDEV_POP(FunctionName.of("stddev_pop")),
   // take top documents from aggregation bucket.
   TAKE(FunctionName.of("take")),
+  // Not always an aggregation query
+  NESTED(FunctionName.of("nested")),
 
   /**
    * Text Functions.

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

@@ -12,6 +12,7 @@
 import lombok.Getter;
 import lombok.Setter;
 import lombok.experimental.UtilityClass;
+import org.apache.commons.lang3.tuple.Pair;
 import org.opensearch.sql.data.model.ExprValue;
 import org.opensearch.sql.data.type.ExprType;
 import org.opensearch.sql.expression.Expression;
@@ -47,6 +48,8 @@ public void register(BuiltinFunctionRepository repository) {
     repository.register(score(BuiltinFunctionName.SCORE));
     repository.register(score(BuiltinFunctionName.SCOREQUERY));
     repository.register(score(BuiltinFunctionName.SCORE_QUERY));
+    // Functions supported in SELECT clause
+    repository.register(nested());
   }
 
   private static FunctionResolver match_bool_prefix() {
@@ -93,6 +96,36 @@ private static FunctionResolver wildcard_query(BuiltinFunctionName wildcardQuery
     return new RelevanceFunctionResolver(funcName);
   }
 
+  private static FunctionResolver nested() {
+    return new FunctionResolver() {
+      @Override
+      public Pair<FunctionSignature, FunctionBuilder> resolve(
+          FunctionSignature unresolvedSignature) {
+        return Pair.of(unresolvedSignature,
+            (functionProperties, arguments) ->
+            new FunctionExpression(BuiltinFunctionName.NESTED.getName(), arguments) {
+              @Override
+              public ExprValue valueOf(Environment<Expression, ExprValue> valueEnv) {
+                return valueEnv.resolve(getArguments().get(0));
+              }
+
+              @Override
+              public ExprType type() {
+                return getArguments().get(0).type();
+              }
+            });
+      }
+
+      @Override
+      public FunctionName getFunctionName() {
+        return BuiltinFunctionName.NESTED.getName();
+      }
+    };
+  }
+
+
+
+
   private static FunctionResolver score(BuiltinFunctionName score) {
     FunctionName funcName = score.getName();
     return new RelevanceFunctionResolver(funcName);

core/src/main/java/org/opensearch/sql/planner/DefaultImplementor.java

@@ -11,6 +11,7 @@
 import org.opensearch.sql.planner.logical.LogicalEval;
 import org.opensearch.sql.planner.logical.LogicalFilter;
 import org.opensearch.sql.planner.logical.LogicalLimit;
+import org.opensearch.sql.planner.logical.LogicalNested;
 import org.opensearch.sql.planner.logical.LogicalPlan;
 import org.opensearch.sql.planner.logical.LogicalPlanNodeVisitor;
 import org.opensearch.sql.planner.logical.LogicalProject;
@@ -26,6 +27,7 @@
 import org.opensearch.sql.planner.physical.EvalOperator;
 import org.opensearch.sql.planner.physical.FilterOperator;
 import org.opensearch.sql.planner.physical.LimitOperator;
+import org.opensearch.sql.planner.physical.NestedOperator;
 import org.opensearch.sql.planner.physical.PhysicalPlan;
 import org.opensearch.sql.planner.physical.ProjectOperator;
 import org.opensearch.sql.planner.physical.RareTopNOperator;
@@ -94,6 +96,11 @@ public PhysicalPlan visitEval(LogicalEval node, C context) {
     return new EvalOperator(visitChild(node, context), node.getExpressions());
   }
 
+  @Override
+  public PhysicalPlan visitNested(LogicalNested node, C context) {
+    return new NestedOperator(visitChild(node, context), node.getFields());
+  }
+
   @Override
   public PhysicalPlan visitSort(LogicalSort node, C context) {
     return new SortOperator(visitChild(node, context), node.getSortList());

core/src/main/java/org/opensearch/sql/planner/logical/LogicalNested.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.planner.logical;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import lombok.EqualsAndHashCode;
+import lombok.Getter;
+import lombok.ToString;
+import org.opensearch.sql.expression.NamedExpression;
+import org.opensearch.sql.expression.ReferenceExpression;
+
+/**
+ * Logical Nested plan.
+ */
+@EqualsAndHashCode(callSuper = true)
+@Getter
+@ToString
+public class LogicalNested extends LogicalPlan {
+  private List<Map<String, ReferenceExpression>> fields;
+  private final List<NamedExpression> projectList;
+
+  /**
+   * Constructor of LogicalNested.
+   *
+   */
+  public LogicalNested(
+      LogicalPlan childPlan,
+      List<Map<String, ReferenceExpression>> fields,
+      List<NamedExpression> projectList
+  ) {
+    super(Collections.singletonList(childPlan));
+    this.fields = fields;
+    this.projectList = projectList;
+  }
+
+  public void addFields(Map<String, ReferenceExpression> fields) {
+    this.fields.add(fields);
+  }
+
+  @Override
+  public <R, C> R accept(LogicalPlanNodeVisitor<R, C> visitor, C context) {
+    return visitor.visitNested(this, context);
+  }
+}

core/src/main/java/org/opensearch/sql/planner/logical/LogicalPlanDSL.java

@@ -74,6 +74,14 @@ public LogicalPlan highlight(LogicalPlan input, Expression field,
     return new LogicalHighlight(input, field, arguments);
   }
 
+
+  public static LogicalPlan nested(
+      LogicalPlan input,
+      List<Map<String, ReferenceExpression>> nestedArgs,
+      List<NamedExpression> projectList) {
+    return new LogicalNested(input, nestedArgs, projectList);
+  }
+
   public static LogicalPlan remove(LogicalPlan input, ReferenceExpression... fields) {
     return new LogicalRemove(input, ImmutableSet.copyOf(fields));
   }

core/src/main/java/org/opensearch/sql/planner/logical/LogicalPlanNodeVisitor.java

@@ -73,6 +73,10 @@ public R visitEval(LogicalEval plan, C context) {
     return visitNode(plan, context);
   }
 
+  public R visitNested(LogicalNested plan, C context) {
+    return visitNode(plan, context);
+  }
+
   public R visitSort(LogicalSort plan, C context) {
     return visitNode(plan, context);
   }

core/src/main/java/org/opensearch/sql/planner/optimizer/LogicalPlanOptimizer.java

@@ -56,6 +56,7 @@ public static LogicalPlanOptimizer create() {
         TableScanPushDown.PUSH_DOWN_SORT,
         TableScanPushDown.PUSH_DOWN_LIMIT,
         TableScanPushDown.PUSH_DOWN_HIGHLIGHT,
+        TableScanPushDown.PUSH_DOWN_NESTED,
         TableScanPushDown.PUSH_DOWN_PROJECT,
         new CreateTableWriteBuilder()));
   }

core/src/main/java/org/opensearch/sql/planner/optimizer/pattern/Patterns.java

@@ -16,6 +16,7 @@
 import org.opensearch.sql.planner.logical.LogicalFilter;
 import org.opensearch.sql.planner.logical.LogicalHighlight;
 import org.opensearch.sql.planner.logical.LogicalLimit;
+import org.opensearch.sql.planner.logical.LogicalNested;
 import org.opensearch.sql.planner.logical.LogicalPlan;
 import org.opensearch.sql.planner.logical.LogicalProject;
 import org.opensearch.sql.planner.logical.LogicalRelation;
@@ -65,6 +66,13 @@ public static <T extends LogicalPlan> Pattern<LogicalHighlight> highlight(Patter
     return Pattern.typeOf(LogicalHighlight.class).with(source(pattern));
   }
 
+  /**
+   * Logical nested operator with a given pattern on inner field.
+   */
+  public static <T extends LogicalPlan> Pattern<LogicalNested> nested(Pattern<T> pattern) {
+    return Pattern.typeOf(LogicalNested.class).with(source(pattern));
+  }
+
   /**
    * Logical project operator with a given pattern on inner field.
    */