A few changes to the expression support.

Makefile.am

@@ -76,6 +76,7 @@ tsdb_SRC := \
 	src/query/QueryUtil.java	\
 	src/query/expression/Absolute.java	\
 	src/query/expression/Expression.java	\
+	src/query/expression/Alias.java	\
 	src/query/expression/DiffSeries.java	\
 	src/query/expression/DivideSeries.java	\
 	src/query/expression/EDPtoDPS.java	\

src/query/expression/Alias.java

@@ -0,0 +1,89 @@
+// This file is part of OpenTSDB.
+// Copyright (C) 2015  The OpenTSDB Authors.
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 2.1 of the License, or (at your
+// option) any later version.  This program is distributed in the hope that it
+// will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty
+// of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
+// General Public License for more details.  You should have received a copy
+// of the GNU Lesser General Public License along with this program.  If not,
+// see <http://www.gnu.org/licenses/>.
+package net.opentsdb.query.expression;
+
+import java.util.List;
+import java.util.Map;
+import com.google.common.base.Joiner;
+
+import net.opentsdb.core.DataPoint;
+import net.opentsdb.core.DataPoints;
+import net.opentsdb.core.MutableDataPoint;
+import net.opentsdb.core.TSQuery;
+
+/**
+ * Returns an alias if provided or the original metric name if not.
+ * @since 2.3
+ */
+public class Alias implements Expression {
+
+    static Joiner COMMA_JOINER = Joiner.on(',').skipNulls();
+
+    @Override
+    public DataPoints[] evaluate(TSQuery data_query, List<DataPoints[]> queryResults,
+                                 List<String> queryParams) {
+        if (queryResults == null || queryResults.size() == 0) {
+            throw new NullPointerException("No query results");
+        }
+
+        String aliasTemplate = "__default";
+
+        if (queryParams != null && queryParams.size() >= 0) {
+            aliasTemplate = COMMA_JOINER.join(queryParams);
+        }
+
+        DataPoints[] inputPoints = queryResults.get(0);
+
+        DataPoint[][] dps = new DataPoint[inputPoints.length][];
+
+        for (int j = 0; j < dps.length; j++) {
+            DataPoints base = inputPoints[j];
+            dps[j] = new DataPoint[base.size()];
+            int i = 0;
+
+            for (DataPoint pt : base) {
+                if (pt.isInteger()) {
+                    dps[j][i] = MutableDataPoint.ofDoubleValue(pt.timestamp(), pt.longValue());
+                } else {
+                    dps[j][i] = MutableDataPoint.ofDoubleValue(pt.timestamp(), pt.doubleValue());
+                }
+                i++;
+            }
+        }
+
+        DataPoints[] resultArray = new DataPoints[queryResults.get(0).length];
+        for (int i = 0; i < resultArray.length; i++) {
+            PostAggregatedDataPoints result = new PostAggregatedDataPoints(inputPoints[i],
+                    dps[i]);
+
+            String alias = aliasTemplate;
+            for (Map.Entry<String, String> e : inputPoints[i].getTags().entrySet()) {
+                alias = alias.replace("@" + e.getKey(), e.getValue());
+            }
+
+            result.setAlias(alias);
+            resultArray[i] = result;
+        }
+
+        return resultArray;
+    }
+
+    @Override
+    public String writeStringField(List<String> queryParams, String innerExpression) {
+        if (queryParams == null || queryParams.size() == 0) {
+            return "NULL";
+        }
+
+        return queryParams.get(0);
+    }
+}

src/query/expression/ExpressionFactory.java

@@ -29,6 +29,7 @@ public final class ExpressionFactory {
       new HashMap<String, Expression>();
 
   static {
+    available_functions.put("alias", new Alias());
     available_functions.put("scale", new Scale());
     available_functions.put("absolute", new Absolute());
     available_functions.put("movingAverage", new MovingAverage());
@@ -46,9 +47,13 @@ private ExpressionFactory() { }
    */
   public static void addTSDBFunctions(final TSDB tsdb) {
     available_functions.put("divideSeries", new DivideSeries(tsdb));
+    available_functions.put("divide", new DivideSeries(tsdb));
     available_functions.put("sumSeries", new SumSeries(tsdb));
+    available_functions.put("sum", new SumSeries(tsdb));
     available_functions.put("diffSeries", new DiffSeries(tsdb));
+    available_functions.put("difference", new DiffSeries(tsdb));
     available_functions.put("multiplySeries", new MultiplySeries(tsdb));
+    available_functions.put("multiply", new MultiplySeries(tsdb));
   }
 
   /**