Support SELECT DISTINCT in new SQL engine

docs/user/dql/basics.rst

@@ -20,7 +20,7 @@ Syntax
 
 The syntax of ``SELECT`` statement is as follows::
 
-  SELECT [DISTINCT] (* | expression) [[AS] alias] [, ...]
+  SELECT [ALL | DISTINCT] (* | expression) [[AS] alias] [, ...]
   FROM index_name
   [WHERE predicates]
   [GROUP BY expression [, ...]
@@ -199,7 +199,7 @@ Result set:
 Example 4: Selecting Distinct Fields
 ------------------------------------
 
-``DISTINCT`` is useful when you want to de-duplicate and get unique field value. You can provide one or more field names.
+By default, ``SELECT ALL`` takes effect to return all rows. ``DISTINCT`` is useful when you want to de-duplicate and get unique field value. You can provide one or more field names ('DISTINCT *' is not supported yet).
 
 SQL query::
 
@@ -255,6 +255,17 @@ Result set:
 | 36|
 +---+
 
+In fact your can use any expression in a ``DISTINCT`` clause as follows::
+
+    od> SELECT DISTINCT SUBSTRING(lastname, 1, 1) FROM accounts;
+    fetched rows / total rows = 3/3
+    +-----------------------------+
+    | SUBSTRING(lastname, 1, 1)   |
+    |-----------------------------|
+    | A                           |
+    | B                           |
+    | D                           |
+    +-----------------------------+
 
 FROM
 ====

integ-test/src/test/resources/correctness/queries/select.txt

@@ -20,3 +20,8 @@ SELECT AvgTicketPrice, Carrier FROM kibana_sample_data_flights WHERE AvgTicketPr
 SELECT AvgTicketPrice, Carrier FROM kibana_sample_data_flights WHERE ABS(AvgTicketPrice * -2) > 1000
 SELECT AvgTicketPrice, Carrier FROM kibana_sample_data_flights WHERE Carrier LIKE 'JetBeat_'
 SELECT AvgTicketPrice, Carrier FROM kibana_sample_data_flights WHERE Carrier LIKE '%Air%'
+SELECT ALL OriginWeather FROM kibana_sample_data_flights
+SELECT DISTINCT OriginWeather FROM kibana_sample_data_flights
+SELECT DISTINCT OriginWeather, FlightDelay FROM kibana_sample_data_flights
+SELECT DISTINCT SUBSTRING(OriginWeather, 1, 1) AS origin FROM kibana_sample_data_flights
+SELECT DISTINCT SUBSTRING(OriginWeather, 1, 1) AS origin, FlightDelay FROM kibana_sample_data_flights

sql/src/main/antlr/OpenDistroSQLParser.g4

@@ -64,7 +64,11 @@ querySpecification
     ;
 
 selectClause
-    : SELECT selectElements
+    : SELECT selectSpec? selectElements
+    ;
+
+selectSpec
+    : (ALL | DISTINCT)
     ;
 
 selectElements

sql/src/main/java/com/amazon/opendistroforelasticsearch/sql/sql/parser/AstAggregationBuilder.java

@@ -27,7 +27,6 @@
 import com.amazon.opendistroforelasticsearch.sql.ast.tree.UnresolvedPlan;
 import com.amazon.opendistroforelasticsearch.sql.common.utils.StringUtils;
 import com.amazon.opendistroforelasticsearch.sql.exception.SemanticCheckException;
-import com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParser.GroupByClauseContext;
 import com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParserBaseVisitor;
 import com.amazon.opendistroforelasticsearch.sql.sql.parser.context.QuerySpecification;
 import java.util.ArrayList;
@@ -42,7 +41,7 @@
  * AST aggregation builder that builds AST aggregation node for the following scenarios:
  *
  *  1. Explicit GROUP BY
- *     1.1 Group by column name or scalar expression:
+ *     1.1 Group by column name or scalar expression (SELECT DISTINCT equivalent):
  *          SELECT ABS(age) FROM test GROUP BY ABS(age)
  *     1.2 Group by alias in SELECT AS clause:
  *          SELECT state AS s FROM test GROUP BY s
@@ -77,18 +76,17 @@ public class AstAggregationBuilder extends OpenDistroSQLParserBaseVisitor<Unreso
 
   @Override
   public UnresolvedPlan visit(ParseTree groupByClause) {
-    if (groupByClause == null) {
+    if (querySpec.getGroupByItems().isEmpty()) {
       if (isAggregatorNotFoundAnywhere()) {
         // Simple select query without GROUP BY and aggregate function in SELECT
         return null;
       }
       return buildImplicitAggregation();
     }
-    return super.visit(groupByClause);
+    return buildExplicitAggregation();
   }
 
-  @Override
-  public UnresolvedPlan visitGroupByClause(GroupByClauseContext ctx) {
+  private UnresolvedPlan buildExplicitAggregation() {
     List<UnresolvedExpression> groupByItems = replaceGroupByItemIfAliasOrOrdinal();
     return new Aggregation(
         new ArrayList<>(querySpec.getAggregators()),

sql/src/main/java/com/amazon/opendistroforelasticsearch/sql/sql/parser/context/QuerySpecification.java

@@ -18,6 +18,7 @@
 
 import static com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParser.GroupByElementContext;
 import static com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParser.OrderByElementContext;
+import static com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParser.SelectClauseContext;
 import static com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParser.SelectElementContext;
 import static com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParser.SubqueryAsRelationContext;
 import static com.amazon.opendistroforelasticsearch.sql.sql.parser.ParserUtils.getTextInQuery;
@@ -34,6 +35,7 @@
 import com.amazon.opendistroforelasticsearch.sql.exception.SemanticCheckException;
 import com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParser.AggregateFunctionCallContext;
 import com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParser.QuerySpecificationContext;
+import com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParser.SelectSpecContext;
 import com.amazon.opendistroforelasticsearch.sql.sql.antlr.parser.OpenDistroSQLParserBaseVisitor;
 import com.amazon.opendistroforelasticsearch.sql.sql.parser.AstExpressionBuilder;
 import java.util.ArrayList;
@@ -181,6 +183,17 @@ public Void visitSubqueryAsRelation(SubqueryAsRelationContext ctx) {
       return null;
     }
 
+    @Override
+    public Void visitSelectClause(SelectClauseContext ctx) {
+      super.visitSelectClause(ctx);
+
+      // SELECT DISTINCT is an equivalent and special form of GROUP BY
+      if (isDistinct(ctx.selectSpec())) {
+        groupByItems.addAll(selectItems);
+      }
+      return null;
+    }
+
     @Override
     public Void visitSelectElement(SelectElementContext ctx) {
       UnresolvedExpression expr = visitAstExpression(ctx.expression());
@@ -215,6 +228,10 @@ public Void visitAggregateFunctionCall(AggregateFunctionCallContext ctx) {
       return super.visitAggregateFunctionCall(ctx);
     }
 
+    private boolean isDistinct(SelectSpecContext ctx) {
+      return (ctx != null) && (ctx.DISTINCT() != null);
+    }
+
     private SortOrder visitSortOrder(Token ctx) {
       if (ctx == null) {
         return null;

sql/src/test/java/com/amazon/opendistroforelasticsearch/sql/sql/antlr/SQLSyntaxParserTest.java

@@ -116,6 +116,12 @@ public void canParseGroupByClause() {
     assertNotNull(parser.parse("SELECT ABS(balance) FROM test GROUP BY 1"));
   }
 
+  @Test
+  public void canParseDistinctClause() {
+    assertNotNull(parser.parse("SELECT DISTINCT name FROM test"));
+    assertNotNull(parser.parse("SELECT DISTINCT name, balance FROM test"));
+  }
+
   @Test
   public void canParseCaseStatement() {
     assertNotNull(parser.parse("SELECT CASE WHEN age > 30 THEN 'age1' ELSE 'age2' END FROM test"));

sql/src/test/java/com/amazon/opendistroforelasticsearch/sql/sql/parser/AstBuilderTest.java

@@ -402,6 +402,54 @@ public void can_build_order_by_multiple_field_names() {
         buildAST("SELECT name, age FROM test ORDER BY name, age DESC"));
   }
 
+  @Test
+  public void can_build_select_distinct_clause() {
+    assertEquals(
+        project(
+            agg(
+                relation("test"),
+                emptyList(),
+                emptyList(),
+                ImmutableList.of(
+                    alias("name", qualifiedName("name")),
+                    alias("age", qualifiedName("age"))),
+                emptyList()),
+            alias("name", qualifiedName("name")),
+            alias("age", qualifiedName("age"))),
+        buildAST("SELECT DISTINCT name, age FROM test"));
+  }
+
+  @Test
+  public void can_build_select_distinct_clause_with_function() {
+    assertEquals(
+        project(
+            agg(
+                relation("test"),
+                emptyList(),
+                emptyList(),
+                ImmutableList.of(
+                    alias("SUBSTRING(name, 1, 2)",
+                        function(
+                            "SUBSTRING",
+                            qualifiedName("name"),
+                            intLiteral(1), intLiteral(2)))),
+                emptyList()),
+            alias("SUBSTRING(name, 1, 2)",
+                function(
+                    "SUBSTRING",
+                    qualifiedName("name"),
+                    intLiteral(1), intLiteral(2)))),
+        buildAST("SELECT DISTINCT SUBSTRING(name, 1, 2) FROM test"));
+  }
+
+  @Test
+  public void can_build_select_all_clause() {
+    assertEquals(
+        buildAST("SELECT name, age FROM test"),
+        buildAST("SELECT ALL name, age FROM test")
+    );
+  }
+
   @Test
   public void can_build_order_by_null_option() {
     assertEquals(