From edf9f2ffb6cdfed3884415e468cdf0b08b63aadd Mon Sep 17 00:00:00 2001
From: Alex Behm <alex.behm@cloudera.com>
Date: Mon, 5 Jun 2017 16:41:53 -0700
Subject: [PATCH] IMPALA-5438: Always eval union const exprs in subplan.

The bug was that the constant exprs of a union were only
evaluated for the first fragment instance. However, for
a union inside a subplan, we should always evaluate the
constant exprs.

Testing:
- Added a regression test.
- Locally ran test_nested_types.py and the union tests in
  test_queries.py

Change-Id: Icd2f21f0213188e2304f8e9536019c7940c07768
Reviewed-on: http://gerrit.cloudera.org:8080/7091
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: Impala Public Jenkins
---
 be/src/exec/union-node.cc                       |  2 +-
 be/src/exec/union-node.h                        |  2 +-
 .../queries/QueryTest/nested-types-subplan.test | 17 ++++++++++++++++-
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/be/src/exec/union-node.cc b/be/src/exec/union-node.cc
index cd16bea57..e1912c9de 100644
--- a/be/src/exec/union-node.cc
+++ b/be/src/exec/union-node.cc
@@ -246,7 +246,7 @@ Status UnionNode::GetNextMaterialized(RuntimeState* state, RowBatch* row_batch)
 }
 
 Status UnionNode::GetNextConst(RuntimeState* state, RowBatch* row_batch) {
-  DCHECK_EQ(state->instance_ctx().per_fragment_instance_idx, 0);
+  DCHECK(state->instance_ctx().per_fragment_instance_idx == 0 || IsInSubplan());
   DCHECK_LT(const_expr_list_idx_, const_expr_lists_.size());
   // Create new tuple buffer for row_batch.
   int64_t tuple_buf_size;
diff --git a/be/src/exec/union-node.h b/be/src/exec/union-node.h
index 311ae1775..79fdfba30 100644
--- a/be/src/exec/union-node.h
+++ b/be/src/exec/union-node.h
@@ -149,7 +149,7 @@ class UnionNode : public ExecNode {
 
   /// Returns true if there are still rows to be returned from constant expressions.
   bool HasMoreConst(const RuntimeState* state) const {
-    return state->instance_ctx().per_fragment_instance_idx == 0 &&
+    return (state->instance_ctx().per_fragment_instance_idx == 0 || IsInSubplan()) &&
         const_expr_list_idx_ < const_expr_lists_.size();
   }
 
diff --git a/testdata/workloads/functional-query/queries/QueryTest/nested-types-subplan.test b/testdata/workloads/functional-query/queries/QueryTest/nested-types-subplan.test
index 9590c1bcd..45116e62b 100644
--- a/testdata/workloads/functional-query/queries/QueryTest/nested-types-subplan.test
+++ b/testdata/workloads/functional-query/queries/QueryTest/nested-types-subplan.test
@@ -577,7 +577,7 @@ where c_custkey = 1
 BIGINT,BIGINT
 ====
 ---- QUERY
-# IMPALA-3678: union in a subplan - passthrough should be disabled.
+# IMPALA-3678: Union in a subplan - passthrough should be disabled.
 select count(c.c_custkey), count(v.tot_price)
 from tpch_nested_parquet.customer c, (
   select sum(o_totalprice) tot_price from c.c_orders
@@ -611,3 +611,18 @@ WHERE ca.o_orderkey < cb.o_orderkey limit 2) v limit 51
 ---- TYPES
 BIGINT
 ====
+---- QUERY
+# IMPALA-5438: Union with constant exprs in a subplan. The 'c_custkey % 100' was chosen
+# to have all impalads produce results to make sure the constant exprs in the union are
+# evaluated regardless of which fragment instance they are in.
+select c_custkey, order_cnt, union_cnt from tpch_nested_parquet.customer c,
+ (select count(o_orderkey) order_cnt from c.c_orders) v,
+ (select count(o_orderkey) union_cnt from (
+  select o_orderkey from c.c_orders
+  union all
+  values(11),(22),(33)) v) v2
+where c_custkey % 100 = 0 and order_cnt != union_cnt - 3;
+---- RESULTS
+---- TYPES
+bigint,bigint,bigint
+====