Support distinct count aggregation

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

@@ -161,8 +161,9 @@ public Expression visitAggregateFunction(AggregateFunction node, AnalysisContext
       Expression arg = node.getField().accept(this, context);
       Aggregator aggregator = (Aggregator) repository.compile(
               builtinFunctionName.get().getName(), Collections.singletonList(arg));
-      if (node.getCondition() != null) {
-        aggregator.condition(analyze(node.getCondition(), context));
+      aggregator.distinct(node.getDistinct());
+      if (node.condition() != null) {
+        aggregator.condition(analyze(node.condition(), context));
       }
       return aggregator;
     } else {

core/src/main/java/org/opensearch/sql/ast/dsl/AstDSL.java

@@ -211,7 +211,16 @@ public static UnresolvedExpression aggregate(
 
   public static UnresolvedExpression filteredAggregate(
       String func, UnresolvedExpression field, UnresolvedExpression condition) {
-    return new AggregateFunction(func, field, condition);
+    return new AggregateFunction(func, field).condition(condition);
+  }
+
+  public static UnresolvedExpression distinctAggregate(String func, UnresolvedExpression field) {
+    return new AggregateFunction(func, field, true);
+  }
+
+  public static UnresolvedExpression filteredDistinctCount(
+      String func, UnresolvedExpression field, UnresolvedExpression condition) {
+    return new AggregateFunction(func, field, true).condition(condition);
   }
 
   public static Function function(String funcName, UnresolvedExpression... funcArgs) {

core/src/main/java/org/opensearch/sql/ast/expression/AggregateFunction.java

@@ -28,9 +28,12 @@
 
 import java.util.Collections;
 import java.util.List;
+import javax.annotation.Nullable;
 import lombok.EqualsAndHashCode;
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
+import lombok.Setter;
+import lombok.experimental.Accessors;
 import org.opensearch.sql.ast.AbstractNodeVisitor;
 import org.opensearch.sql.common.utils.StringUtils;
 
@@ -45,7 +48,10 @@ public class AggregateFunction extends UnresolvedExpression {
   private final String funcName;
   private final UnresolvedExpression field;
   private final List<UnresolvedExpression> argList;
+  @Setter
+  @Accessors(fluent = true)
   private UnresolvedExpression condition;
+  private Boolean distinct = false;
 
   /**
    * Constructor.
@@ -62,14 +68,13 @@ public AggregateFunction(String funcName, UnresolvedExpression field) {
    * Constructor.
    * @param funcName function name.
    * @param field {@link UnresolvedExpression}.
-   * @param condition condition in aggregation filter.
+   * @param distinct whether distinct field is specified or not.
    */
-  public AggregateFunction(String funcName, UnresolvedExpression field,
-                           UnresolvedExpression condition) {
+  public AggregateFunction(String funcName, UnresolvedExpression field, Boolean distinct) {
     this.funcName = funcName;
     this.field = field;
     this.argList = Collections.emptyList();
-    this.condition = condition;
+    this.distinct = distinct;
   }
 
   @Override

core/src/main/java/org/opensearch/sql/data/model/ExprValueUtils.java

@@ -157,6 +157,14 @@ public static ExprValue fromObjectValue(Object o, ExprCoreType type) {
     }
   }
 
+  public static Byte getByteValue(ExprValue exprValue) {
+    return exprValue.byteValue();
+  }
+
+  public static Short getShortValue(ExprValue exprValue) {
+    return exprValue.shortValue();
+  }
+
   public static Integer getIntegerValue(ExprValue exprValue) {
     return exprValue.integerValue();
   }

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

@@ -500,6 +500,10 @@ public Aggregator count(Expression... expressions) {
     return aggregate(BuiltinFunctionName.COUNT, expressions);
   }
 
+  public Aggregator distinctCount(Expression... expressions) {
+    return count(expressions).distinct(true);
+  }
+
   public Aggregator varSamp(Expression... expressions) {
     return aggregate(BuiltinFunctionName.VARSAMP, expressions);
   }

core/src/main/java/org/opensearch/sql/expression/aggregation/Aggregator.java

@@ -64,6 +64,10 @@ public abstract class Aggregator<S extends AggregationState>
   @Getter
   @Accessors(fluent = true)
   protected Expression condition;
+  @Setter
+  @Getter
+  @Accessors(fluent = true)
+  protected Boolean distinct = false;
 
   /**
    * Create an {@link AggregationState} which will be used for aggregation.

core/src/main/java/org/opensearch/sql/expression/aggregation/CountAggregator.java

@@ -28,8 +28,10 @@
 
 import static org.opensearch.sql.utils.ExpressionUtils.format;
 
+import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
+import java.util.Set;
 import org.opensearch.sql.data.model.ExprValue;
 import org.opensearch.sql.data.model.ExprValueUtils;
 import org.opensearch.sql.data.type.ExprCoreType;
@@ -50,7 +52,7 @@ public CountAggregator.CountState create() {
 
   @Override
   protected CountState iterate(ExprValue value, CountState state) {
-    state.count++;
+    state.count(value, distinct);
     return state;
   }
 
@@ -64,11 +66,23 @@ public String toString() {
    */
   protected static class CountState implements AggregationState {
     private int count;
+    private final Set<ExprValue> distinctValues = new HashSet<>();
 
     CountState() {
       this.count = 0;
     }
 
+    public void count(ExprValue value, Boolean distinct) {
+      if (distinct) {
+        if (!distinctValues.contains(value)) {
+          distinctValues.add(value);
+          count++;
+        }
+      } else {
+        count++;
+      }
+    }
+
     @Override
     public ExprValue result() {
       return ExprValueUtils.integerValue(count);

core/src/main/java/org/opensearch/sql/expression/aggregation/NamedAggregator.java

@@ -54,8 +54,8 @@ public class NamedAggregator extends Aggregator<AggregationState> {
 
   /**
    * NamedAggregator.
-   * The aggregator properties {@link #condition} is inherited by named aggregator
-   * to avoid errors introduced by the property inconsistency.
+   * The aggregator properties {@link #condition} and {@link #distinct}
+   * are inherited by named aggregator to avoid errors introduced by the property inconsistency.
    *
    * @param name name
    * @param delegated delegated
@@ -67,6 +67,7 @@ public NamedAggregator(
     this.name = name;
     this.delegated = delegated;
     this.condition = delegated.condition;
+    this.distinct = delegated.distinct;
   }
 
   @Override

core/src/test/java/org/opensearch/sql/analysis/ExpressionAnalyzerTest.java

@@ -300,6 +300,24 @@ public void variance_mapto_varPop() {
     );
   }
 
+  @Test
+  public void distinct_count() {
+    assertAnalyzeEqual(
+        dsl.distinctCount(DSL.ref("integer_value", INTEGER)),
+        AstDSL.distinctAggregate("count", qualifiedName("integer_value"))
+    );
+  }
+
+  @Test
+  public void filtered_distinct_count() {
+    assertAnalyzeEqual(
+        dsl.distinctCount(DSL.ref("integer_value", INTEGER))
+            .condition(dsl.greater(DSL.ref("integer_value", INTEGER), DSL.literal(1))),
+        AstDSL.filteredDistinctCount("count", qualifiedName("integer_value"), function(
+            ">", qualifiedName("integer_value"), intLiteral(1)))
+    );
+  }
+
   protected Expression analyze(UnresolvedExpression unresolvedExpression) {
     return expressionAnalyzer.analyze(unresolvedExpression, analysisContext);
   }

core/src/test/java/org/opensearch/sql/data/model/ExprValueUtilsTest.java

@@ -96,8 +96,8 @@ public class ExprValueUtilsTest {
       Lists.newArrayList(Iterables.concat(numberValues, nonNumberValues));
 
   private static List<Function<ExprValue, Object>> numberValueExtractor = Arrays.asList(
-      ExprValue::byteValue,
-      ExprValue::shortValue,
+      ExprValueUtils::getByteValue,
+      ExprValueUtils::getShortValue,
       ExprValueUtils::getIntegerValue,
       ExprValueUtils::getLongValue,
       ExprValueUtils::getFloatValue,

core/src/test/java/org/opensearch/sql/expression/aggregation/AggregationTest.java

@@ -116,6 +116,13 @@ public class AggregationTest extends ExpressionTestBase {
                   "timestamp_value",
                   "2040-01-01 07:00:00")));
 
+  protected static List<ExprValue> tuples_with_duplicates =
+      Arrays.asList(
+          ExprValueUtils.tupleValue(ImmutableMap.of("integer_value", 1, "double_value", 4d)),
+          ExprValueUtils.tupleValue(ImmutableMap.of("integer_value", 1, "double_value", 3d)),
+          ExprValueUtils.tupleValue(ImmutableMap.of("integer_value", 2, "double_value", 2d)),
+          ExprValueUtils.tupleValue(ImmutableMap.of("integer_value", 3, "double_value", 1d)));
+
   protected static List<ExprValue> tuples_with_null_and_missing =
       Arrays.asList(
           ExprValueUtils.tupleValue(

core/src/test/java/org/opensearch/sql/expression/aggregation/CountAggregatorTest.java

@@ -129,6 +129,21 @@ public void filtered_count() {
     assertEquals(3, result.value());
   }
 
+  @Test
+  public void distinct_count() {
+    ExprValue result = aggregation(dsl.distinctCount(DSL.ref("integer_value", INTEGER)),
+        tuples_with_duplicates);
+    assertEquals(3, result.value());
+  }
+
+  @Test
+  public void filtered_distinct_count() {
+    ExprValue result = aggregation(dsl.distinctCount(DSL.ref("integer_value", INTEGER))
+        .condition(dsl.greater(DSL.ref("double_value", DOUBLE), DSL.literal(1d))),
+        tuples_with_duplicates);
+    assertEquals(2, result.value());
+  }
+
   @Test
   public void count_with_missing() {
     ExprValue result = aggregation(dsl.count(DSL.ref("integer_value", INTEGER)),

docs/user/dql/aggregations.rst

@@ -357,6 +357,19 @@ Example::
     | 2.8613807855648994 |
     +--------------------+
 
+DISTINCT COUNT Aggregation
+--------------------------
+
+To get the count of distinct values of a field, you can add a keyword ``DISTINCT`` before the field in the count aggregation. Example::
+
+    os> SELECT COUNT(DISTINCT gender), COUNT(gender) FROM accounts;
+    fetched rows / total rows = 1/1
+    +--------------------------+-----------------+
+    | COUNT(DISTINCT gender)   | COUNT(gender)   |
+    |--------------------------+-----------------|
+    | 2                        | 4               |
+    +--------------------------+-----------------+
+
 HAVING Clause
 =============
 
@@ -456,3 +469,16 @@ The ``FILTER`` clause can be used in aggregation functions without GROUP BY as w
     | 4            | 1          |
     +--------------+------------+
 
+Distinct count aggregate with FILTER
+------------------------------------
+
+The ``FILTER`` clause is also used in distinct count to do the filtering before count the distinct values of specific field. For example::
+
+    os> SELECT COUNT(DISTINCT firstname) FILTER(WHERE age > 30) AS distinct_count FROM accounts
+    fetched rows / total rows = 1/1
+    +------------------+
+    | distinct_count   |
+    |------------------|
+    | 3                |
+    +------------------+
+

docs/user/ppl/cmd/stats.rst

@@ -302,3 +302,18 @@ PPL query::
     | 36         | 32         | M        |
     +------------+------------+----------+
 
+Example 7: Calculate the distinct count of a field
+==================================================
+
+To get the count of distinct values of a field, you can use ``DISTINCT_COUNT`` (or ``DC``) function instead of ``COUNT``. The example calculates both the count and the distinct count of gender field of all the accounts.
+
+PPL query::
+
+    os> source=accounts | stats count(gender), distinct_count(gender);
+    fetched rows / total rows = 1/1
+    +-----------------+--------------------------+
+    | count(gender)   | distinct_count(gender)   |
+    |-----------------+--------------------------|
+    | 4               | 2                        |
+    +-----------------+--------------------------+
+

integ-test/src/test/java/org/opensearch/sql/ppl/StatsCommandIT.java

@@ -77,6 +77,19 @@ public void testStatsCountAll() throws IOException {
     verifyDataRows(response, rows(1000));
   }
 
+  @Test
+  public void testStatsDistinctCount() throws IOException {
+    JSONObject response =
+        executeQuery(String.format("source=%s | stats distinct_count(gender)", TEST_INDEX_ACCOUNT));
+    verifySchema(response, schema("distinct_count(gender)", null, "integer"));
+    verifyDataRows(response, rows(2));
+
+    response =
+        executeQuery(String.format("source=%s | stats dc(age)", TEST_INDEX_ACCOUNT));
+    verifySchema(response, schema("dc(age)", null, "integer"));
+    verifyDataRows(response, rows(21));
+  }
+
   @Test
   public void testStatsMin() throws IOException {
     JSONObject response = executeQuery(String.format(

integ-test/src/test/java/org/opensearch/sql/sql/AggregationIT.java

@@ -30,7 +30,15 @@ protected void init() throws Exception {
   }
 
   @Test
-  void filteredAggregateWithSubquery() throws IOException {
+  void filteredAggregatePushedDown() throws IOException {
+    JSONObject response = executeQuery(
+        "SELECT COUNT(*) FILTER(WHERE age > 35) FROM " + TEST_INDEX_BANK);
+    verifySchema(response, schema("COUNT(*)", null, "integer"));
+    verifyDataRows(response, rows(3));
+  }
+
+  @Test
+  void filteredAggregateNotPushedDown() throws IOException {
     JSONObject response = executeQuery(
         "SELECT COUNT(*) FILTER(WHERE age > 35) FROM (SELECT * FROM " + TEST_INDEX_BANK
             + ") AS a");