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
ABSTRACT SYNTAX TREE:
  (TOK_QUERY (TOK_FROM (TOK_SUBQUERY (TOK_UNION (TOK_UNION (TOK_QUERY (TOK_FROM (TOK_TABREF (TOK_TABNAME src) s1)) (TOK_INSERT (TOK_DESTINATION (TOK_DIR TOK_TMP_FILE)) (TOK_SELECT (TOK_SELEXPR (. (TOK_TABLE_OR_COL s1) key) key) (TOK_SELEXPR (. (TOK_TABLE_OR_COL s1) value) value)))) (TOK_QUERY (TOK_FROM (TOK_TABREF (TOK_TABNAME src) s2)) (TOK_INSERT (TOK_DESTINATION (TOK_DIR TOK_TMP_FILE)) (TOK_SELECT (TOK_SELEXPR (. (TOK_TABLE_OR_COL s2) key) key) (TOK_SELEXPR (. (TOK_TABLE_OR_COL s2) value) value))))) (TOK_QUERY (TOK_FROM (TOK_TABREF (TOK_TABNAME src) s3)) (TOK_INSERT (TOK_DESTINATION (TOK_DIR TOK_TMP_FILE)) (TOK_SELECT (TOK_SELEXPR (. (TOK_TABLE_OR_COL s3) key) key) (TOK_SELEXPR (. (TOK_TABLE_OR_COL s3) value) value))))) unionsrc)) (TOK_INSERT (TOK_DESTINATION (TOK_DIR TOK_TMP_FILE)) (TOK_SELECT (TOK_SELEXPR (TOK_FUNCTION count 1)))))

STAGE DEPENDENCIES:
  Stage-1 is a root stage
  Stage-0 is a root stage

STAGE PLANS:
  Stage: Stage-1
    Map Reduce
      Alias -> Map Operator Tree:
        null-subquery1-subquery1:unionsrc-subquery1-subquery1:s1 
          TableScan
            alias: s1
            Select Operator
              expressions:
                    expr: key
                    type: string
                    expr: value
                    type: string
              outputColumnNames: _col0, _col1
              Union
                Select Operator
                  Group By Operator
                    aggregations:
                          expr: count(1)
                    bucketGroup: false
                    mode: hash
                    outputColumnNames: _col0
                    Reduce Output Operator
                      sort order: 
                      tag: -1
                      value expressions:
                            expr: _col0
                            type: bigint
        null-subquery1-subquery2:unionsrc-subquery1-subquery2:s2 
          TableScan
            alias: s2
            Select Operator
              expressions:
                    expr: key
                    type: string
                    expr: value
                    type: string
              outputColumnNames: _col0, _col1
              Union
                Select Operator
                  Group By Operator
                    aggregations:
                          expr: count(1)
                    bucketGroup: false
                    mode: hash
                    outputColumnNames: _col0
                    Reduce Output Operator
                      sort order: 
                      tag: -1
                      value expressions:
                            expr: _col0
                            type: bigint
        null-subquery2:unionsrc-subquery2:s3 
          TableScan
            alias: s3
            Select Operator
              expressions:
                    expr: key
                    type: string
                    expr: value
                    type: string
              outputColumnNames: _col0, _col1
              Union
                Select Operator
                  Group By Operator
                    aggregations:
                          expr: count(1)
                    bucketGroup: false
                    mode: hash
                    outputColumnNames: _col0
                    Reduce Output Operator
                      sort order: 
                      tag: -1
                      value expressions:
                            expr: _col0
                            type: bigint
      Reduce Operator Tree:
        Group By Operator
          aggregations:
                expr: count(VALUE._col0)
          bucketGroup: false
          mode: mergepartial
          outputColumnNames: _col0
          Select Operator
            expressions:
                  expr: _col0
                  type: bigint
            outputColumnNames: _col0
            File Output Operator
              compressed: false
              GlobalTableId: 0
              table:
                  input format: org.apache.hadoop.mapred.TextInputFormat
                  output format: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat

  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