ASTERIXDB-1005, ASTERIXDB-1263: Clean up subplan flattening:
1. Inline NestedTupleSource and remove SubplanOperator for special cases that
   join operators inside the SubplanOperator can be re-targeted for
   correlations;
2. Blindly inline NestedTupleSource and remove SubplanOperator for general cases
   where the condition of the special case is not met.

Change-Id: I4dd130a25f3c81272cc23f844ea20e376e990612
Reviewed-on: https://asterix-gerrit.ics.uci.edu/579
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Till Westmann <tillw@apache.org>
diff --git a/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1018.plan b/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1018.plan
index 7c4a8c2..1e7e505 100644
--- a/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1018.plan
+++ b/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1018.plan
@@ -4,75 +4,76 @@
       -- ASSIGN  |PARTITIONED|
         -- STREAM_PROJECT  |PARTITIONED|
           -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-            -- HYBRID_HASH_JOIN [$$39][$$34]  |PARTITIONED|
+            -- HYBRID_HASH_JOIN [$$34][$$50]  |PARTITIONED|
               -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
                 -- STREAM_PROJECT  |PARTITIONED|
                   -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
                     -- DATASOURCE_SCAN  |PARTITIONED|
                       -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
                         -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
-              -- HASH_PARTITION_EXCHANGE [$$34]  |PARTITIONED|
+              -- HASH_PARTITION_EXCHANGE [$$50]  |PARTITIONED|
                 -- STREAM_PROJECT  |PARTITIONED|
                   -- ASSIGN  |PARTITIONED|
-                    -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                      -- PRE_CLUSTERED_GROUP_BY[$$41]  |PARTITIONED|
-                              {
-                                -- AGGREGATE  |LOCAL|
-                                  -- STREAM_SELECT  |LOCAL|
-                                    -- NESTED_TUPLE_SOURCE  |LOCAL|
-                              }
-                        -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                          -- STABLE_SORT [$$41(ASC)]  |PARTITIONED|
-                            -- HASH_PARTITION_EXCHANGE [$$41]  |PARTITIONED|
-                              -- STREAM_PROJECT  |PARTITIONED|
-                                -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                  -- NESTED_LOOP  |PARTITIONED|
-                                    -- BROADCAST_EXCHANGE  |PARTITIONED|
-                                      -- STREAM_PROJECT  |PARTITIONED|
-                                        -- STREAM_SELECT  |PARTITIONED|
-                                          -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                            -- PRE_CLUSTERED_GROUP_BY[$$47]  |PARTITIONED|
-                                                    {
-                                                      -- AGGREGATE  |LOCAL|
-                                                        -- STREAM_SELECT  |LOCAL|
-                                                          -- NESTED_TUPLE_SOURCE  |LOCAL|
-                                                    }
-                                              -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                                -- STABLE_SORT [$$47(ASC)]  |PARTITIONED|
-                                                  -- HASH_PARTITION_EXCHANGE [$$47]  |PARTITIONED|
-                                                    -- STREAM_PROJECT  |PARTITIONED|
-                                                      -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                                        -- HYBRID_HASH_JOIN [$$45][$$42]  |PARTITIONED|
-                                                          -- HASH_PARTITION_EXCHANGE [$$45]  |PARTITIONED|
-                                                            -- NESTED_LOOP  |PARTITIONED|
-                                                              -- BROADCAST_EXCHANGE  |PARTITIONED|
-                                                                -- STREAM_PROJECT  |PARTITIONED|
-                                                                  -- ASSIGN  |PARTITIONED|
-                                                                    -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                                                      -- DATASOURCE_SCAN  |PARTITIONED|
-                                                                        -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                                                          -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
-                                                              -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                                                -- STREAM_PROJECT  |PARTITIONED|
-                                                                  -- ASSIGN  |PARTITIONED|
-                                                                    -- STREAM_PROJECT  |PARTITIONED|
+                    -- STREAM_PROJECT  |PARTITIONED|
+                      -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                        -- PRE_CLUSTERED_GROUP_BY[$$55, $$24, $$54]  |PARTITIONED|
+                                {
+                                  -- AGGREGATE  |LOCAL|
+                                    -- STREAM_SELECT  |LOCAL|
+                                      -- NESTED_TUPLE_SOURCE  |LOCAL|
+                                }
+                          -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                            -- STABLE_SORT [$$55(ASC), $$24(ASC), $$54(ASC)]  |PARTITIONED|
+                              -- HASH_PARTITION_EXCHANGE [$$55, $$24, $$54]  |PARTITIONED|
+                                -- STREAM_PROJECT  |PARTITIONED|
+                                  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                    -- NESTED_LOOP  |PARTITIONED|
+                                      -- BROADCAST_EXCHANGE  |PARTITIONED|
+                                        -- STREAM_PROJECT  |PARTITIONED|
+                                          -- STREAM_SELECT  |PARTITIONED|
+                                            -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                              -- PRE_CLUSTERED_GROUP_BY[$$49, $$35]  |PARTITIONED|
+                                                      {
+                                                        -- AGGREGATE  |LOCAL|
+                                                          -- STREAM_SELECT  |LOCAL|
+                                                            -- NESTED_TUPLE_SOURCE  |LOCAL|
+                                                      }
+                                                -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                  -- STABLE_SORT [$$49(ASC), $$35(ASC)]  |PARTITIONED|
+                                                    -- HASH_PARTITION_EXCHANGE [$$49, $$35]  |PARTITIONED|
+                                                      -- STREAM_PROJECT  |PARTITIONED|
+                                                        -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                          -- HYBRID_HASH_JOIN [$$47][$$38]  |PARTITIONED|
+                                                            -- HASH_PARTITION_EXCHANGE [$$47]  |PARTITIONED|
+                                                              -- NESTED_LOOP  |PARTITIONED|
+                                                                -- BROADCAST_EXCHANGE  |PARTITIONED|
+                                                                  -- STREAM_PROJECT  |PARTITIONED|
+                                                                    -- ASSIGN  |PARTITIONED|
                                                                       -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
                                                                         -- DATASOURCE_SCAN  |PARTITIONED|
                                                                           -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
                                                                             -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
-                                                          -- HASH_PARTITION_EXCHANGE [$$42]  |PARTITIONED|
-                                                            -- STREAM_PROJECT  |PARTITIONED|
-                                                              -- ASSIGN  |PARTITIONED|
-                                                                -- STREAM_PROJECT  |PARTITIONED|
-                                                                  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                                                    -- DATASOURCE_SCAN  |PARTITIONED|
-                                                                      -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                                                        -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
-                                    -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                      -- STREAM_PROJECT  |PARTITIONED|
-                                        -- ASSIGN  |PARTITIONED|
-                                          -- STREAM_PROJECT  |PARTITIONED|
-                                            -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                              -- DATASOURCE_SCAN  |PARTITIONED|
-                                                -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
-                                                  -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
+                                                                -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                                  -- ASSIGN  |PARTITIONED|
+                                                                    -- STREAM_PROJECT  |PARTITIONED|
+                                                                      -- ASSIGN  |PARTITIONED|
+                                                                        -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                                          -- DATASOURCE_SCAN  |PARTITIONED|
+                                                                            -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                                              -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
+                                                            -- HASH_PARTITION_EXCHANGE [$$38]  |PARTITIONED|
+                                                              -- STREAM_PROJECT  |PARTITIONED|
+                                                                -- ASSIGN  |PARTITIONED|
+                                                                  -- STREAM_PROJECT  |PARTITIONED|
+                                                                    -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                                      -- DATASOURCE_SCAN  |PARTITIONED|
+                                                                        -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                                          -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
+                                      -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                        -- STREAM_PROJECT  |PARTITIONED|
+                                          -- ASSIGN  |PARTITIONED|
+                                            -- STREAM_PROJECT  |PARTITIONED|
+                                              -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                -- DATASOURCE_SCAN  |PARTITIONED|
+                                                  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                    -- EMPTY_TUPLE_SOURCE  |PARTITIONED|