PREHOOK: query: -- union case: all subqueries are a map-only jobs, 3 way union, same input for all sub-queries, followed by reducesink

explain 
  select count(1) FROM (select s1.key as key, s1.value as value from src s1 UNION  ALL  
                        select s2.key as key, s2.value as value from src s2 UNION ALL
                        select s3.key as key, s3.value as value from src s3) unionsrc
PREHOOK: type: QUERY
POSTHOOK: query: -- union case: all subqueries are a map-only jobs, 3 way union, same input for all sub-queries, followed by reducesink

explain 
  select count(1) FROM (select s1.key as key, s1.value as value from src s1 UNION  ALL  
                        select s2.key as key, s2.value as value from src s2 UNION ALL
                        select s3.key as key, s3.value as value from src s3) unionsrc
POSTHOOK: type: QUERY
STAGE DEPENDENCIES:
  Stage-1 is a root stage
  Stage-0 is a root stage

STAGE PLANS:
  Stage: Stage-1
    Tez
      Edges:
        Map 1 <- Union 2 (CONTAINS)
        Map 4 <- Union 2 (CONTAINS)
        Map 5 <- Union 2 (CONTAINS)
        Reducer 3 <- Union 2 (SIMPLE_EDGE)
#### A masked pattern was here ####
      Vertices:
        Map 1 
            Map Operator Tree:
                TableScan
                  alias: s1
                  Select Operator
                    expressions: key (type: string), value (type: string)
                    outputColumnNames: _col0, _col1
                    Select Operator
                      Group By Operator
                        aggregations: count(1)
                        mode: hash
                        outputColumnNames: _col0
                        Reduce Output Operator
                          sort order: 
                          value expressions: _col0 (type: bigint)
        Map 4 
            Map Operator Tree:
                TableScan
                  alias: s2
                  Select Operator
                    expressions: key (type: string), value (type: string)
                    outputColumnNames: _col0, _col1
                    Select Operator
                      Group By Operator
                        aggregations: count(1)
                        mode: hash
                        outputColumnNames: _col0
                        Reduce Output Operator
                          sort order: 
                          value expressions: _col0 (type: bigint)
        Map 5 
            Map Operator Tree:
                TableScan
                  alias: s3
                  Select Operator
                    expressions: key (type: string), value (type: string)
                    outputColumnNames: _col0, _col1
                    Select Operator
                      Group By Operator
                        aggregations: count(1)
                        mode: hash
                        outputColumnNames: _col0
                        Reduce Output Operator
                          sort order: 
                          value expressions: _col0 (type: bigint)
        Reducer 3 
            Reduce Operator Tree:
              Group By Operator
                aggregations: count(VALUE._col0)
                mode: mergepartial
                outputColumnNames: _col0
                Statistics: Num rows: 1 Data size: 8 Basic stats: COMPLETE Column stats: NONE
                Select Operator
                  expressions: _col0 (type: bigint)
                  outputColumnNames: _col0
                  Statistics: Num rows: 1 Data size: 8 Basic stats: COMPLETE Column stats: NONE
                  File Output Operator
                    compressed: false
                    Statistics: Num rows: 1 Data size: 8 Basic stats: COMPLETE Column stats: NONE
                    table:
                        input format: org.apache.hadoop.mapred.TextInputFormat
                        output format: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
                        serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
        Union 2 
            Vertex: Union 2

  Stage: Stage-0
    Fetch Operator
      limit: -1

PREHOOK: query: select count(1) FROM (select s1.key as key, s1.value as value from src s1 UNION  ALL  
                        select s2.key as key, s2.value as value from src s2 UNION ALL
                        select s3.key as key, s3.value as value from src s3) unionsrc
PREHOOK: type: QUERY
PREHOOK: Input: default@src
#### A masked pattern was here ####
POSTHOOK: query: select count(1) FROM (select s1.key as key, s1.value as value from src s1 UNION  ALL  
                        select s2.key as key, s2.value as value from src s2 UNION ALL
                        select s3.key as key, s3.value as value from src s3) unionsrc
POSTHOOK: type: QUERY
POSTHOOK: Input: default@src
#### A masked pattern was here ####
1500