Index: openjpa-jdbc/src/main/java/org/apache/openjpa/jdbc/sql/SelectImpl.java
===================================================================
--- openjpa-jdbc/src/main/java/org/apache/openjpa/jdbc/sql/SelectImpl.java	(revision 564449)
+++ openjpa-jdbc/src/main/java/org/apache/openjpa/jdbc/sql/SelectImpl.java	(working copy)
@@ -1373,9 +1373,12 @@
         getJoins(joins, true);
         if (_grouping == null)
             _grouping = new SQLBuffer(_dict);
-        else
-            _grouping.append(", ");
-        _grouping.append(sql);
+
+        if (_grouping.getSQL().indexOf(sql.getSQL()) < 0) {
+            if (!_grouping.isEmpty())
+                _grouping.append(", ");
+            _grouping.append(sql.getSQL());
+        }
     }
 
     public void groupBy(String sql) {
@@ -1386,9 +1389,12 @@
         getJoins(joins, true);
         if (_grouping == null)
             _grouping = new SQLBuffer(_dict);
-        else
-            _grouping.append(", ");
-        _grouping.append(sql);
+        
+        if (_grouping.getSQL().indexOf(sql) < 0) {
+            if (!_grouping.isEmpty())
+                _grouping.append(", ");
+            _grouping.append(sql);
+        }
     }
 
     public void groupBy(Column col) {
@@ -1398,11 +1404,13 @@
     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 (_grouping.getSQL().indexOf(getColumnAlias(col, pj)) < 0) {
+            if (!_grouping.isEmpty())
+                _grouping.append(", ");
+            _grouping.append(getColumnAlias(col, pj));
+        }
     }
 
     public void groupBy(Column[] cols) {
@@ -1412,14 +1420,14 @@
     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 (_grouping.getSQL().indexOf(getColumnAlias(cols[i], pj)) < 0) {
+                if (!_grouping.isEmpty())
+                    _grouping.append(", ");
+                _grouping.append(getColumnAlias(cols[i], pj));
+            }
         }
     }