Empty Over Clause should trigger Union-Exchange to be added below

0: jdbc:drill:drillbit=localhost> select * from t1;
+-------+--------+-------------+
|  a1   |   b1   |     c1      |
+-------+--------+-------------+
| 1     | aaaaa  | 2015-01-01  |
| 2     | bbbbb  | 2015-01-02  |
| 3     | ccccc  | 2015-01-03  |
| 4     | null   | 2015-01-04  |
| 5     | eeeee  | 2015-01-05  |
| 6     | fffff  | 2015-01-06  |
| 7     | ggggg  | 2015-01-07  |
| null  | hhhhh  | 2015-01-08  |
| 9     | iiiii  | null        |
| 10    | jjjjj  | 2015-01-10  |
+-------+--------+-------------+
10 rows selected (0.087 seconds)

0: jdbc:drill:drillbit=localhost> select
. . . . . . . . . . . . . . . . >         a1,
. . . . . . . . . . . . . . . . >         sum(a1) over(partition by b1, c1),
. . . . . . . . . . . . . . . . >         sum(a1) over()
. . . . . . . . . . . . . . . . > from
. . . . . . . . . . . . . . . . >         t1
. . . . . . . . . . . . . . . . > order by
. . . . . . . . . . . . . . . . >         a1;
+-------+---------+---------+
|  a1   | EXPR$1  | EXPR$2  |
+-------+---------+---------+
| 1     | 1       | 6       |
| 2     | 2       | 6       |
| 3     | 3       | 6       |
| 4     | 4       | 19      |
| 5     | 5       | 22      |
| 6     | 6       | 19      |
| 7     | 7       | 22      |
| 9     | 9       | 19      |
| 10    | 10      | 22      |
| null  | null    | 6       |
+-------+---------+---------+
10 rows selected (0.165 seconds)

0: jdbc:drill:drillbit=localhost> explain plan for select
. . . . . . . . . . . . . . . . >         a1,
. . . . . . . . . . . . . . . . >         sum(a1) over(partition by b1, c1),
. . . . . . . . . . . . . . . . >         sum(a1) over()
. . . . . . . . . . . . . . . . > from
. . . . . . . . . . . . . . . . >         t1
. . . . . . . . . . . . . . . . > order by
. . . . . . . . . . . . . . . . >         a1;
+------+------+
| text | json |
+------+------+
| 00-00    Screen
00-01      ProjectAllowDup(a1=[$0], EXPR$1=[$1], EXPR$2=[$2])
00-02        SingleMergeExchange(sort0=[0 ASC])
01-01          SelectionVectorRemover
01-02            Sort(sort0=[$0], dir0=[ASC])
01-03              Project(a1=[$0], w0$o0=[$1], w1$o0=[$2])
01-04                HashToRandomExchange(dist0=[[$0]])
02-01                  UnorderedMuxExchange
03-01                    Project(a1=[$0], w0$o0=[$1], w1$o0=[$2], E_X_P_R_H_A_S_H_F_I_E_L_D=[castInt(hash64AsDouble($0))])
03-02                      Project(a1=[$1], w0$o0=[$4], w1$o0=[$5])
03-03                        Window(window#0=[window(partition {} order by [] range between UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING aggs [SUM($1)])])
03-04                          Window(window#0=[window(partition {2, 3} order by [] range between UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING aggs [SUM($1)])])
03-05                            SelectionVectorRemover
03-06                              Sort(sort0=[$2], sort1=[$3], dir0=[ASC], dir1=[ASC])
03-07                                Project(T154¦¦*=[$0], a1=[$1], b1=[$2], c1=[$3])
03-08                                  HashToRandomExchange(dist0=[[$2]], dist1=[[$3]])
04-01                                    UnorderedMuxExchange
05-01                                      Project(T154¦¦*=[$0], a1=[$1], b1=[$2], c1=[$3], E_X_P_R_H_A_S_H_F_I_E_L_D=[castInt(hash64AsDouble($3, hash64AsDouble($2)))])
05-02                                        Project(T154¦¦*=[$0], a1=[$1], b1=[$2], c1=[$3])
05-03                                          Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath [path=file:/Users/vmarkman/drill/testdata/subqueries/t1]], selectionRoot=file:/Users/vmarkman/drill/testdata/subqueries/t1, numFiles=1, columns=[`*`]]])

0: jdbc:drill:drillbit=localhost> select
. . . . . . . . . . . . . . . . >         a1,
. . . . . . . . . . . . . . . . >         sum(a1) over(partition by b1, c1),
. . . . . . . . . . . . . . . . >         sum(a1) over()
. . . . . . . . . . . . . . . . > from
. . . . . . . . . . . . . . . . >         t1
. . . . . . . . . . . . . . . . > order by
. . . . . . . . . . . . . . . . >         a1;
+-------+---------+---------+
|  a1   | EXPR$1  | EXPR$2  |
+-------+---------+---------+
| 1     | 1       | 47      |
| 2     | 2       | 47      |
| 3     | 3       | 47      |
| 4     | 4       | 47      |
| 5     | 5       | 47      |
| 6     | 6       | 47      |
| 7     | 7       | 47      |
| 9     | 9       | 47      |
| 10    | 10      | 47      |
| null  | null    | 47      |
+-------+---------+---------+
10 rows selected (0.117 seconds)

0: jdbc:drill:drillbit=localhost> explain plan for select
. . . . . . . . . . . . . . . . >         a1,
. . . . . . . . . . . . . . . . >         sum(a1) over(partition by b1, c1),
. . . . . . . . . . . . . . . . >         sum(a1) over()
. . . . . . . . . . . . . . . . > from
. . . . . . . . . . . . . . . . >         t1
. . . . . . . . . . . . . . . . > order by
. . . . . . . . . . . . . . . . >         a1;
+------+------+
| text | json |
+------+------+
| 00-00    Screen
00-01      ProjectAllowDup(a1=[$0], EXPR$1=[$1], EXPR$2=[$2])
00-02        SelectionVectorRemover
00-03          Sort(sort0=[$0], dir0=[ASC])
00-04            Project(a1=[$1], w0$o0=[$4], w1$o0=[$5])
00-05              Window(window#0=[window(partition {} order by [] range between UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING aggs [SUM($1)])])
00-06                Window(window#0=[window(partition {2, 3} order by [] range between UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING aggs [SUM($1)])])
00-07                  SelectionVectorRemover
00-08                    Sort(sort0=[$2], sort1=[$3], dir0=[ASC], dir1=[ASC])
00-09                      Project(T157¦¦*=[$0], a1=[$1], b1=[$2], c1=[$3])
00-10                        Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath [path=file:/Users/vmarkman/drill/testdata/subqueries/t1]], selectionRoot=file:/Users/vmarkman/drill/testdata/subqueries/t1, numFiles=1, columns=[`*`]]])

alter session set `planner.slice_target` = 1;

select
        a1,
        sum(a1) over(partition by b1, c1),
        sum(a1) over()
from
        t1
order by
        a1;