Index: org/apache/openjpa/jdbc/sql/SelectImpl.java
===================================================================
--- org/apache/openjpa/jdbc/sql/SelectImpl.java	(revision 566280)
+++ org/apache/openjpa/jdbc/sql/SelectImpl.java	(working copy)
@@ -124,6 +124,7 @@
     // combined list of selected ids and map of each id to its alias
     protected final Selects _selects = newSelects();
     private List _ordered = null;
+    private List _grouped = null;
 
     // flags
     private int _flags = 0;
@@ -1371,11 +1372,16 @@
 
     public void groupBy(SQLBuffer sql, Joins joins) {
         getJoins(joins, true);
-        if (_grouping == null)
-            _grouping = new SQLBuffer(_dict);
-        else
-            _grouping.append(", ");
-        _grouping.append(sql);
+        if (_grouped == null || !_grouped.contains(sql.getSQL())) {
+            if (_grouping == null) {
+                _grouping = new SQLBuffer(_dict);
+                _grouped = new ArrayList();
+            } else
+                _grouping.append(", ");
+
+            _grouping.append(sql.getSQL());
+            _grouped.add(sql.getSQL());
+        }
     }
 
     public void groupBy(String sql) {
@@ -1384,11 +1390,16 @@
 
     public void groupBy(String sql, Joins joins) {
         getJoins(joins, true);
-        if (_grouping == null)
-            _grouping = new SQLBuffer(_dict);
-        else
-            _grouping.append(", ");
-        _grouping.append(sql);
+        if (_grouped == null || !_grouped.contains(sql)) {
+            if (_grouping == null) {
+                _grouping = new SQLBuffer(_dict);
+                _grouped = new ArrayList();
+            } else
+                _grouping.append(", ");
+            
+            _grouping.append(sql);
+            _grouped.add(sql);
+        }
     }
 
     public void groupBy(Column col) {
@@ -1396,13 +1407,17 @@
     }
 
     public void groupBy(Column col, Joins joins) {
-        if (_grouping == null)
-            _grouping = new SQLBuffer(_dict);
-        else
-            _grouping.append(", ");
-
         PathJoins pj = getJoins(joins, true);
-        _grouping.append(getColumnAlias(col, pj));
+        if (_grouped == null || !_grouped.contains(getColumnAlias(col, pj))) {
+            if (_grouping == null) {
+                _grouping = new SQLBuffer(_dict);
+                _grouped = new ArrayList();
+            } else
+                _grouping.append(", ");
+            
+            _grouping.append(getColumnAlias(col, pj));
+            _grouped.add(getColumnAlias(col, pj));
+        }
     }
 
     public void groupBy(Column[] cols) {
@@ -1410,16 +1425,19 @@
     }
 
     public void groupBy(Column[] cols, Joins joins) {
-        if (_grouping == null)
-            _grouping = new SQLBuffer(_dict);
-        else
-            _grouping.append(", ");
-
         PathJoins pj = getJoins(joins, true);
         for (int i = 0; i < cols.length; i++) {
-            if (i > 0)
-                _grouping.append(", ");
-            _grouping.append(getColumnAlias(cols[i], pj));
+            if (_grouped == null
+                || !_grouped.contains(getColumnAlias(cols[i], pj))) {
+                if (_grouping == null) {
+                    _grouping = new SQLBuffer(_dict);
+                    _grouped = new ArrayList();
+                } else
+                    _grouping.append(", ");
+                
+                _grouping.append(getColumnAlias(cols[i], pj));
+                _grouped.add(getColumnAlias(cols[i], pj));
+            }
         }
     }