fix: restore DISTINCT operator (#129)

* restore DISTINCT operator

* address review comments

Author: SrikarMannepalli

document-store/src/main/java/org/hypertrace/core/documentstore/expression/operators/AggregationOperator.java

@@ -3,6 +3,9 @@
 public enum AggregationOperator {
   AVG,
   COUNT,
+  /** @deprecated Use {@link AggregationOperator#DISTINCT_ARRAY} instead. */
+  @Deprecated(forRemoval = true)
+  DISTINCT,
   DISTINCT_ARRAY, // This operator generates an array of distinct values
   DISTINCT_COUNT,
   SUM,

document-store/src/main/java/org/hypertrace/core/documentstore/mongo/parser/MongoAggregateExpressionParser.java

@@ -3,6 +3,7 @@
 import static java.util.Collections.unmodifiableMap;
 import static org.hypertrace.core.documentstore.expression.operators.AggregationOperator.AVG;
 import static org.hypertrace.core.documentstore.expression.operators.AggregationOperator.COUNT;
+import static org.hypertrace.core.documentstore.expression.operators.AggregationOperator.DISTINCT;
 import static org.hypertrace.core.documentstore.expression.operators.AggregationOperator.DISTINCT_ARRAY;
 import static org.hypertrace.core.documentstore.expression.operators.AggregationOperator.MAX;
 import static org.hypertrace.core.documentstore.expression.operators.AggregationOperator.MIN;
@@ -23,6 +24,7 @@ final class MongoAggregateExpressionParser extends MongoSelectTypeExpressionPars
           new EnumMap<>(AggregationOperator.class) {
             {
               put(AVG, "$avg");
+              put(DISTINCT, "$addToSet");
               put(DISTINCT_ARRAY, "$addToSet");
               put(SUM, "$sum");
               put(MIN, "$min");

document-store/src/main/java/org/hypertrace/core/documentstore/postgres/query/v1/vistors/PostgresAggregateExpressionVisitor.java

@@ -59,6 +59,8 @@ public String visit(final AggregateExpression expression) {
   private String convertToAggregationFunction(AggregationOperator operator, String value) {
     if (operator.equals(AggregationOperator.DISTINCT_COUNT)) {
       return String.format("COUNT(DISTINCT %s )", value);
+    } else if (operator.equals(AggregationOperator.DISTINCT)) {
+      return String.format("ARRAY_AGG(DISTINCT %s)", value);
     } else if (operator.equals(AggregationOperator.DISTINCT_ARRAY)) {
       return String.format("ARRAY_AGG(DISTINCT %s)", value);
     }