fix: parse PostgreSQL GROUP BY DISTINCT

Author: 2748109647

src/main/java/net/sf/jsqlparser/statement/select/GroupByElement.java

@@ -33,11 +33,21 @@ public enum SortDirection {
     private List<ExpressionList<Expression>> groupingSets = new ArrayList<>();
     // postgres rollup is an ExpressionList
     private boolean mysqlWithRollup = false;
+    private boolean distinct = false;
 
     public boolean isUsingBrackets() {
         return groupByExpressions.isUsingBrackets();
     }
 
+    public boolean isDistinct() {
+        return distinct;
+    }
+
+    public GroupByElement setDistinct(boolean distinct) {
+        this.distinct = distinct;
+        return this;
+    }
+
     public <T, S> T accept(GroupByVisitor<T> groupByVisitor, S context) {
         return groupByVisitor.visit(this, context);
     }
@@ -115,6 +125,9 @@ public String toString() {
     public void appendTo(StringBuilder builder, Consumer<ExpressionList<?>> listRenderer,
             Consumer<Expression> expressionRenderer) {
         builder.append("GROUP BY ");
+        if (distinct) {
+            builder.append("DISTINCT ");
+        }
         if (groupByExpressions != null) {
             if (hasGroupBySortDirections()) {
                 appendOrderedExpressions(builder, expressionRenderer);

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -10452,6 +10452,7 @@ GroupByElement GroupByColumnReferences():
 }
 {
     <K_GROUP> <K_BY>
+    [ LOOKAHEAD(<K_DISTINCT>) <K_DISTINCT> { groupBy.setDistinct(true); } ]
     (
         LOOKAHEAD(2) (
             <K_GROUPING> <K_SETS>

src/test/java/net/sf/jsqlparser/statement/select/SelectTest.java

@@ -4792,6 +4792,13 @@ public void testGroupingSets3() throws JSQLParserException {
                 "SELECT COL_1 FROM TABLE_1 GROUP BY GROUPING SETS (COL_1, ())");
     }
 
+    @Test
+    public void testGroupingSetsDistinctIssue2785() throws JSQLParserException {
+        PlainSelect select = (PlainSelect) assertSqlCanBeParsedAndDeparsed(
+                "SELECT 1 GROUP BY DISTINCT GROUPING SETS ((1), (1))");
+        assertTrue(select.getGroupBy().isDistinct());
+    }
+
     @Test
     public void testLongQualifiedNamesIssue763() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed(