add more comments in code

Signed-off-by: Lantao Jin <ltjin@amazon.com>

Author: LantaoJin

core/src/main/java/org/opensearch/sql/calcite/utils/PlanUtils.java

@@ -616,6 +616,7 @@ static void addIgnoreNullBucketHintToAggregate(RelBuilder relBuilder) {
                 .build());
   }
 
+  /** Extract the RexLiteral from the aggregate call if the aggregate call is a LITERAL_AGG. */
   static @Nullable RexLiteral getObjectFromLiteralAgg(AggregateCall aggCall) {
     if (aggCall.getAggregation().kind == SqlKind.LITERAL_AGG) {
       return (RexLiteral)

opensearch/src/main/java/org/opensearch/sql/opensearch/data/value/OpenSearchExprValueFactory.java

@@ -38,7 +38,6 @@
 import java.util.function.BiFunction;
 import lombok.Getter;
 import lombok.Setter;
-import org.apache.commons.lang3.function.TriFunction;
 import org.opensearch.OpenSearchParseException;
 import org.opensearch.common.time.DateFormatter;
 import org.opensearch.common.time.DateFormatters;
@@ -136,52 +135,6 @@ public void extendTypeMapping(Map<String, OpenSearchDataType> typeMapping) {
               (c, dt) -> new OpenSearchExprBinaryValue(c.stringValue()))
           .build();
 
-  private static final Map<ExprType, TriFunction<Content, ExprType, Boolean, ExprValue>>
-      typeActionMap2 =
-          new ImmutableMap.Builder<ExprType, TriFunction<Content, ExprType, Boolean, ExprValue>>()
-              .put(
-                  OpenSearchDataType.of(OpenSearchDataType.MappingType.Integer),
-                  (c, dt, a) -> new ExprIntegerValue(c.intValue()))
-              .put(
-                  OpenSearchDataType.of(OpenSearchDataType.MappingType.Long),
-                  (c, dt, a) -> new ExprLongValue(c.longValue()))
-              .put(
-                  OpenSearchDataType.of(OpenSearchDataType.MappingType.Short),
-                  (c, dt, a) -> new ExprShortValue(c.shortValue()))
-              .put(
-                  OpenSearchDataType.of(OpenSearchDataType.MappingType.Byte),
-                  (c, dt, a) -> new ExprByteValue(c.byteValue()))
-              .put(
-                  OpenSearchDataType.of(OpenSearchDataType.MappingType.Float),
-                  (c, dt, a) -> new ExprFloatValue(c.floatValue()))
-              .put(
-                  OpenSearchDataType.of(OpenSearchDataType.MappingType.Double),
-                  (c, dt, a) -> new ExprDoubleValue(c.doubleValue()))
-              .put(
-                  OpenSearchTextType.of(),
-                  (c, dt, a) -> new OpenSearchExprTextValue(c.stringValue()))
-              .put(
-                  OpenSearchDataType.of(OpenSearchDataType.MappingType.Keyword),
-                  (c, dt, a) -> new ExprStringValue(c.stringValue()))
-              .put(
-                  OpenSearchDataType.of(OpenSearchDataType.MappingType.Boolean),
-                  (c, dt, a) -> ExprBooleanValue.of(c.booleanValue()))
-              // Handles the creation of DATE, TIME & DATETIME
-              .put(
-                  OpenSearchDateType.of(TIME), OpenSearchExprValueFactory::createOpenSearchDateType)
-              .put(
-                  OpenSearchDateType.of(DATE), OpenSearchExprValueFactory::createOpenSearchDateType)
-              .put(
-                  OpenSearchDateType.of(TIMESTAMP),
-                  OpenSearchExprValueFactory::createOpenSearchDateType)
-              .put(
-                  OpenSearchDateType.of(OpenSearchDataType.MappingType.Ip),
-                  (c, dt, a) -> new ExprIpValue(c.stringValue()))
-              .put(
-                  OpenSearchDataType.of(OpenSearchDataType.MappingType.Binary),
-                  (c, dt, a) -> new OpenSearchExprBinaryValue(c.stringValue()))
-              .build();
-
   /** Constructor of OpenSearchExprValueFactory. */
   public OpenSearchExprValueFactory(
       Map<String, OpenSearchDataType> typeMapping, boolean fieldTypeTolerance) {

opensearch/src/main/java/org/opensearch/sql/opensearch/planner/rules/DedupPushdownRule.java

@@ -141,6 +141,10 @@ && dedupColumnsContainRexCall(rexCallsExceptWindow, dedupColumns)) {
     LogicalProject childProject = (LogicalProject) relBuilder.peek();
 
     // 3. Push an Aggregate
+    // We push down a LITERAL_AGG with dedupNumer for converting the dedup command to aggregate:
+    // (1) Pass the dedupNumer to AggregateAnalyzer.processAggregateCalls()
+    // (2) Distinguish it from an optimization operator and user defined aggregator.
+    // (LITERAL_AGG is used in optimization normally, see {@link SqlKind#LITERAL_AGG})
     final List<RexNode> newDedupColumns = RexUtil.apply(mappingForDedupColumns, dedupColumns);
     relBuilder.aggregate(relBuilder.groupKey(newDedupColumns), relBuilder.literalAgg(dedupNumer));
     PlanUtils.addIgnoreNullBucketHintToAggregate(relBuilder);

opensearch/src/main/java/org/opensearch/sql/opensearch/request/AggregateAnalyzer.java

@@ -335,7 +335,7 @@ private static Pair<Builder, List<MetricParser>> processAggregateCalls(
 
     for (int i = 0; i < aggCalls.size(); i++) {
       AggregateCall aggCall = aggCalls.get(i);
-      List<RexNode> args = convertAggArgThroughProject(aggCall, project, helper);
+      List<RexNode> args = convertAggArgThroughProject(aggCall, project);
       String aggFieldName = aggFieldNames.get(i);
 
       Pair<AggregationBuilder, MetricParser> builderAndParser =
@@ -347,8 +347,16 @@ private static Pair<Builder, List<MetricParser>> processAggregateCalls(
     return Pair.of(metricBuilder, metricParserList);
   }
 
-  private static List<RexNode> convertAggArgThroughProject(
-      AggregateCall aggCall, Project project, AggregateAnalyzer.AggregateBuilderHelper helper) {
+  /**
+   * Convert aggregate arguments through child project. Normally, just return the rex nodes of
+   * Project which are included in aggCall expression. If the aggCall is a LITERAL_AGG, it returns
+   * all rex nodes of Project except WindowFunction.
+   *
+   * @param aggCall the aggregate call
+   * @param project the project
+   * @return the converted RexNode list
+   */
+  private static List<RexNode> convertAggArgThroughProject(AggregateCall aggCall, Project project) {
     return project == null
         ? List.of()
         : PlanUtils.getObjectFromLiteralAgg(aggCall) != null
@@ -546,6 +554,7 @@ yield switch (functionName) {
               String.format("Unsupported push-down aggregator %s", aggCall.getAggregation()));
         }
         Integer dedupNumber = literal.getValueAs(Integer.class);
+        // Disable fetchSource since TopHitsParser only parses fetchField currently.
         TopHitsAggregationBuilder topHitsAggregationBuilder =
             AggregationBuilders.topHits(aggFieldName).from(0).fetchSource(false).size(dedupNumber);
         args.stream()