feat(parser): support opt-in legacy MySQL GROUP BY ordering

Preserve ASC/DESC by grouping-list position and share AST/deparser rendering. Keep existing expression traversal and make appending grouping expressions preserve both the expression list and its directions.

Fixes #1169.

Author: minleejae

README.md

@@ -189,6 +189,9 @@ out. `is()` answers "did the grammar prove it", `may()` answers "could it be rul
 guard uses `may()` and a dispatcher uses `is()`. Function volatility is not a syntactic property,
 so anything the caller has not declared pure stays unproven and is listed by name.
 
+Legacy MySQL `GROUP BY ... ASC/DESC` is available with `Dialect.MYSQL` and the explicit
+`withLegacyMySqlGroupBy(true)` option; modern/default parsing keeps it disabled.
+
 ## Piped SQL
 
 Support is progressing for Piped SQL, which writes queries in the order they actually

src/main/java/net/sf/jsqlparser/parser/AbstractJSqlParser.java

@@ -102,6 +102,11 @@ public P withUnsupportedStatements(boolean allowUnsupportedStatements) {
         return withFeature(Feature.allowUnsupportedStatements, allowUnsupportedStatements);
     }
 
+    /** Enables GROUP BY ASC/DESC for MySQL versions before 8.0.13. Requires MYSQL dialect. */
+    public P withLegacyMySqlGroupBy(boolean enabled) {
+        return withFeature(Feature.allowLegacyMySqlGroupBy, enabled);
+    }
+
     public P withTimeOut(long timeOutMillSeconds) {
         return withFeature(Feature.timeOut, timeOutMillSeconds);
     }

src/main/java/net/sf/jsqlparser/parser/feature/Feature.java

@@ -75,6 +75,8 @@ public enum Feature {
      * "GROUP BY"
      */
     selectGroupBy,
+    /** Explicit ASC/DESC on GROUP BY items in legacy MySQL. */
+    selectGroupByOrdering,
     /**
      * "GROUPING SETS"
      */
@@ -784,6 +786,9 @@ public enum Feature {
      */
     allowPostgresSpecificSyntax(false),
 
+    /** Enables legacy GROUP BY ordering with the MYSQL dialect; disabled by default. */
+    allowLegacyMySqlGroupBy(false),
+
     // PERFORMANCE
 
     /**

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

@@ -16,12 +16,19 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
+import java.util.Objects;
+import java.util.function.Consumer;
 
 import net.sf.jsqlparser.expression.Expression;
 import net.sf.jsqlparser.expression.operators.relational.ExpressionList;
 import net.sf.jsqlparser.expression.operators.relational.ParenthesedExpressionList;
 
 public class GroupByElement implements Serializable {
+    public enum SortDirection {
+        ASC, DESC
+    }
+
+    private final List<SortDirection> groupBySortDirections = new ArrayList<>();
     private ExpressionList<Expression> groupByExpressions = new ExpressionList<>();
     private List<ExpressionList<Expression>> groupingSets = new ArrayList<>();
     // postgres rollup is an ExpressionList
@@ -45,6 +52,9 @@ public ExpressionList<Expression> getGroupByExpressions() {
     }
 
     public void setGroupByExpressions(ExpressionList<Expression> groupByExpressions) {
+        if (this.groupByExpressions != groupByExpressions) {
+            groupBySortDirections.clear();
+        }
         this.groupByExpressions = groupByExpressions;
     }
 
@@ -68,35 +78,83 @@ public void addGroupingSet(ExpressionList<Expression> list) {
         this.groupingSets.add(list);
     }
 
+    /** Returns the explicit direction at a grouping-list position, or null if omitted. */
+    public SortDirection getGroupBySortDirection(int index) {
+        Objects.checkIndex(index, groupByExpressions.size());
+        return index < groupBySortDirections.size() ? groupBySortDirections.get(index) : null;
+    }
+
+    /** Directions belong to list positions. Replacing the expression list clears them. */
+    public void setGroupBySortDirection(int index, SortDirection direction) {
+        Objects.checkIndex(index, groupByExpressions.size());
+        while (groupBySortDirections.size() <= index) {
+            groupBySortDirections.add(null);
+        }
+        groupBySortDirections.set(index, direction);
+    }
+
+    public boolean hasGroupBySortDirections() {
+        if (groupByExpressions != null && !groupBySortDirections.isEmpty()) {
+            for (int i = 0; i < groupByExpressions.size(); i++) {
+                if (getGroupBySortDirection(i) != null) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
     @Override
-    @SuppressWarnings({"PMD.CyclomaticComplexity"})
     public String toString() {
-        StringBuilder b = new StringBuilder();
-        b.append("GROUP BY ");
+        StringBuilder builder = new StringBuilder();
+        appendTo(builder, builder::append, builder::append);
+        return builder.toString();
+    }
 
+    /** Shares clause layout while letting a deparser visit each expression. */
+    public void appendTo(StringBuilder builder, Consumer<ExpressionList<?>> listRenderer,
+            Consumer<Expression> expressionRenderer) {
+        builder.append("GROUP BY ");
         if (groupByExpressions != null) {
-            b.append(groupByExpressions);
+            if (hasGroupBySortDirections()) {
+                appendOrderedExpressions(builder, expressionRenderer);
+            } else {
+                listRenderer.accept(groupByExpressions);
+            }
         }
-
-        int i = 0;
         if (!groupingSets.isEmpty()) {
-            if (b.charAt(b.length() - 1) != ' ') {
-                b.append(' ');
+            if (builder.charAt(builder.length() - 1) != ' ') {
+                builder.append(' ');
             }
-            b.append("GROUPING SETS (");
-            for (ExpressionList<?> expressionList : groupingSets) {
-                b.append(i++ > 0 ? ", " : "").append(Select.getStringList(
-                        expressionList,
-                        true, expressionList instanceof ParenthesedExpressionList));
+            builder.append("GROUPING SETS (");
+            for (int i = 0; i < groupingSets.size(); i++) {
+                builder.append(i > 0 ? ", " : "");
+                listRenderer.accept(groupingSets.get(i));
             }
-            b.append(")");
+            builder.append(")");
         }
-
         if (isMysqlWithRollup()) {
-            b.append(" WITH ROLLUP");
+            builder.append(" WITH ROLLUP");
         }
+    }
 
-        return b.toString();
+    private void appendOrderedExpressions(StringBuilder builder,
+            Consumer<Expression> expressionRenderer) {
+        boolean brackets = groupByExpressions instanceof ParenthesedExpressionList<?>;
+        if (brackets) {
+            builder.append('(');
+        }
+        for (int i = 0; i < groupByExpressions.size(); i++) {
+            builder.append(i > 0 ? ", " : "");
+            expressionRenderer.accept(groupByExpressions.get(i));
+            SortDirection direction = getGroupBySortDirection(i);
+            if (direction != null) {
+                builder.append(' ').append(direction);
+            }
+        }
+        if (brackets) {
+            builder.append(')');
+        }
     }
 
     public GroupByElement withGroupByExpressions(ExpressionList<Expression> groupByExpressions) {
@@ -115,9 +173,9 @@ public GroupByElement addGroupByExpressions(Expression... groupByExpressions) {
 
     public GroupByElement addGroupByExpressions(
             Collection<? extends Expression> groupByExpressions) {
-        ExpressionList collection =
-                Optional.ofNullable(getGroupByExpressions()).orElseGet(ExpressionList::new);
-        Collections.addAll(collection, groupByExpressions);
+        ExpressionList<Expression> collection =
+                Optional.ofNullable(getGroupByExpressionList()).orElseGet(ExpressionList::new);
+        collection.addAll(groupByExpressions);
         return this.withGroupByExpressions(collection);
     }
 

src/main/java/net/sf/jsqlparser/util/deparser/GroupByDeParser.java

@@ -10,41 +10,24 @@
 package net.sf.jsqlparser.util.deparser;
 
 import net.sf.jsqlparser.expression.ExpressionVisitor;
-import net.sf.jsqlparser.expression.operators.relational.ExpressionList;
 import net.sf.jsqlparser.statement.select.GroupByElement;
 
 public class GroupByDeParser extends AbstractDeParser<GroupByElement> {
 
     private final ExpressionListDeParser<?> expressionListDeParser;
+    private final ExpressionVisitor<StringBuilder> expressionVisitor;
 
     public GroupByDeParser(ExpressionVisitor<StringBuilder> expressionVisitor,
             StringBuilder buffer) {
         super(buffer);
+        this.expressionVisitor = expressionVisitor;
         this.expressionListDeParser = new ExpressionListDeParser<>(expressionVisitor, buffer);
         this.builder = buffer;
     }
 
     @Override
-    @SuppressWarnings({"PMD.CyclomaticComplexity", "PMD.NPathComplexity"})
     public void deParse(GroupByElement groupBy) {
-        builder.append("GROUP BY ");
-        expressionListDeParser.deParse(groupBy.getGroupByExpressionList());
-
-        int i = 0;
-        if (!groupBy.getGroupingSets().isEmpty()) {
-            if (builder.charAt(builder.length() - 1) != ' ') {
-                builder.append(' ');
-            }
-            builder.append("GROUPING SETS (");
-            for (ExpressionList<?> expressionList : groupBy.getGroupingSets()) {
-                builder.append(i++ > 0 ? ", " : "");
-                expressionListDeParser.deParse(expressionList);
-            }
-            builder.append(")");
-        }
-
-        if (groupBy.isMysqlWithRollup()) {
-            builder.append(" WITH ROLLUP");
-        }
+        groupBy.appendTo(builder, expressionListDeParser::deParse,
+                expression -> expression.accept(expressionVisitor, null));
     }
 }

src/main/java/net/sf/jsqlparser/util/validation/validator/GroupByValidator.java

@@ -31,6 +31,9 @@ public void validate(GroupByElement groupBy) {
     public <S> Void visit(GroupByElement groupBy, S context) {
         for (ValidationCapability c : getCapabilities()) {
             validateFeature(c, Feature.selectGroupBy);
+            if (groupBy.hasGroupBySortDirections()) {
+                validateFeature(c, Feature.selectGroupByOrdering);
+            }
             if (isNotEmpty(groupBy.getGroupingSets())) {
                 validateFeature(c, Feature.selectGroupByGroupingSets);
             }

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

@@ -7596,7 +7596,13 @@ GroupByElement GroupByColumnReferences():
         )
         |
         (
-            list = ExpressionList() { groupBy.setGroupByExpressions(list); }
+            (
+                LOOKAHEAD({ getAsBoolean(Feature.allowLegacyMySqlGroupBy)
+                        && "MYSQL".equals(getAsString(Feature.dialect)) })
+                LegacyMySqlGroupByExpressions(groupBy)
+                |
+                list = ExpressionList() { groupBy.setGroupByExpressions(list); }
+            )
             (
                 LOOKAHEAD(2) <K_GROUPING> <K_SETS>
                 "("
@@ -7612,6 +7618,27 @@ GroupByElement GroupByColumnReferences():
     }
 }
 
+void LegacyMySqlGroupByExpressions(GroupByElement groupBy):
+{}
+{
+    LegacyMySqlGroupByExpression(groupBy)
+    ( LOOKAHEAD(2) "," LegacyMySqlGroupByExpression(groupBy) )*
+}
+
+void LegacyMySqlGroupByExpression(GroupByElement groupBy):
+{
+    Expression expression;
+    Token direction;
+}
+{
+    expression = Expression() { groupBy.getGroupByExpressionList().add(expression); }
+    [ LOOKAHEAD(2) (direction=<K_ASC> | direction=<K_DESC>) {
+        groupBy.setGroupBySortDirection(groupBy.getGroupByExpressionList().size() - 1,
+                direction.kind == K_ASC ? GroupByElement.SortDirection.ASC
+                        : GroupByElement.SortDirection.DESC);
+    } ]
+}
+
 ExpressionList<Expression> GroupingSet():
 {
     ExpressionList<Expression> list;

src/site/sphinx/usage.rst

@@ -872,3 +872,21 @@ References: `CREATE ROLE <https://www.postgresql.org/docs/18/sql-createrole.html
 `REVOKE <https://www.postgresql.org/docs/18/sql-revoke.html>`_,
 `ALTER DEFAULT PRIVILEGES <https://www.postgresql.org/docs/18/sql-alterdefaultprivileges.html>`_,
 `CREATE TRIGGER <https://www.postgresql.org/docs/18/sql-createtrigger.html>`_.
+
+Legacy MySQL GROUP BY ordering
+==============================
+
+MySQL before 8.0.13 accepted ``ASC`` and ``DESC`` on individual ``GROUP BY`` items.
+Select the existing ``MYSQL`` dialect and explicitly enable this legacy syntax:
+
+.. code-block:: java
+
+    Statement statement = CCJSqlParserUtil.parse(
+        "SELECT a FROM t GROUP BY a DESC",
+        parser -> parser.withDialect(Dialect.MYSQL).withLegacyMySqlGroupBy(true));
+
+The option is disabled by default and does not enable this syntax in other dialects.
+``GroupByElement`` keeps its existing expression list; ``getGroupBySortDirection(index)``
+returns each explicit direction, or null when omitted. Directions follow list positions;
+replacing the expression list clears them. Validators report the separate
+``selectGroupByOrdering`` feature, which is not enabled in the MySQL 8.0 capability.