diff --git a/algebricks/algebricks-rewriter/src/main/java/edu/uci/ics/hyracks/algebricks/rewriter/rules/EliminateGroupByEmptyKeyRule.java b/algebricks/algebricks-rewriter/src/main/java/edu/uci/ics/hyracks/algebricks/rewriter/rules/EliminateGroupByEmptyKeyRule.java
new file mode 100644
index 0000000..e93fdd1
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+++ b/algebricks/algebricks-rewriter/src/main/java/edu/uci/ics/hyracks/algebricks/rewriter/rules/EliminateGroupByEmptyKeyRule.java
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2009-2013 by The Regents of the University of California
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * you may obtain a copy of the License from
+ * 
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package edu.uci.ics.hyracks.algebricks.rewriter.rules;
+
+import java.util.List;
+
+import org.apache.commons.lang3.mutable.Mutable;
+
+import edu.uci.ics.hyracks.algebricks.common.exceptions.AlgebricksException;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.ILogicalOperator;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.ILogicalPlan;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.IOptimizationContext;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.LogicalOperatorTag;
+import edu.uci.ics.hyracks.algebricks.core.algebra.base.LogicalVariable;
+import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
+import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.GroupByOperator;
+import edu.uci.ics.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
+
+/**
+ * This rule lift out the aggregate operator out from a group-by operator
+ * if the gby operator groups-by on empty key, e.g., the group-by variables are empty.
+ * 
+ * @author yingyib
+ */
+public class EliminateGroupByEmptyKeyRule implements IAlgebraicRewriteRule {
+
+    @Override
+    public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context) throws AlgebricksException {
+        return false;
+    }
+
+    @Override
+    public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
+            throws AlgebricksException {
+        AbstractLogicalOperator op = (AbstractLogicalOperator) opRef.getValue();
+        if (op.getOperatorTag() != LogicalOperatorTag.GROUP) {
+            return false;
+        }
+        GroupByOperator groupOp = (GroupByOperator) op;
+        List<LogicalVariable> groupVars = groupOp.getGbyVarList();
+        if (groupVars.size() > 0) {
+            return false;
+        }
+        List<ILogicalPlan> nestedPlans = groupOp.getNestedPlans();
+        if (nestedPlans.size() > 1) {
+            return false;
+        }
+        ILogicalPlan nestedPlan = nestedPlans.get(0);
+        if (nestedPlan.getRoots().size() > 1) {
+            return false;
+        }
+        Mutable<ILogicalOperator> topOpRef = nestedPlan.getRoots().get(0);
+        ILogicalOperator topOp = nestedPlan.getRoots().get(0).getValue();
+        Mutable<ILogicalOperator> nestedTupleSourceRef = getNestedTupleSourceReference(topOpRef);
+        /**
+         * connect nested top op into the plan
+         */
+        opRef.setValue(topOp);
+        /**
+         * connect child op into the plan
+         */
+        nestedTupleSourceRef.setValue(groupOp.getInputs().get(0).getValue());
+        return true;
+    }
+
+    private Mutable<ILogicalOperator> getNestedTupleSourceReference(Mutable<ILogicalOperator> nestedTopOperatorRef) {
+        Mutable<ILogicalOperator> currentOpRef = nestedTopOperatorRef;
+        while (currentOpRef.getValue().getInputs() != null && currentOpRef.getValue().getInputs().size() > 0) {
+            currentOpRef = currentOpRef.getValue().getInputs().get(0);
+        }
+        return currentOpRef;
+    }
+
+}