TAJO-913: Add some missed tests for constant value group-by keys.

tajo-core/src/test/java/org/apache/tajo/engine/query/TestGroupByQuery.java

@@ -138,6 +138,23 @@ public final void testGroupByWithSameConstantKeys1() throws Exception {
     cleanupQuery(res);
   }
 
+  @Test
+  public final void testGroupByWithConstantKeys1() throws Exception {
+    // select 123 as key, count(1) as total from lineitem group by key order by key, total;
+    ResultSet res = executeQuery();
+    assertResultSet(res);
+    cleanupQuery(res);
+  }
+
+  @Test
+  public final void testGroupByWithConstantKeys2() throws Exception {
+    // select l_partkey as a, timestamp '2014-07-07 04:28:31.561' as b, '##' as c, count(*) d from lineitem
+    // group by a, b, c;
+    ResultSet res = executeQuery();
+    assertResultSet(res);
+    cleanupQuery(res);
+  }
+
   @Test
   public final void testDistinctAggregation1() throws Exception {
     // select l_orderkey, max(l_orderkey) as maximum, count(distinct l_linenumber) as unique_key from lineitem

tajo-core/src/test/resources/queries/TestGroupByQuery/testGroupByWithConstantKeys2.sql

@@ -0,0 +1 @@
+select l_partkey as a, timestamp '2014-07-07 04:28:31.561' as b, '##' as c, count(*) d from lineitem group by a, b, c;

tajo-core/src/test/resources/results/TestGroupByQuery/testGroupByWithConstantKeys1.result

@@ -0,0 +1,3 @@
+key,total
+-------------------------------
+123,5

tajo-core/src/test/resources/results/TestGroupByQuery/testGroupByWithConstantKeys2.result

@@ -0,0 +1,5 @@
+a,b,c,d
+-------------------------------
+3,2014-07-07 04:28:31.561,##,1
+1,2014-07-07 04:28:31.561,##,2
+2,2014-07-07 04:28:31.561,##,2