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

explain 
  select unionsrc.key, count(1) FROM (select 'tst1' as key, count(1) as value from src s1
                                        UNION  ALL  
                                            select 'tst2' as key, count(1) as value from src s2
                                        UNION ALL
                                            select 'tst3' as key, count(1) as value from src s3) unionsrc group by unionsrc.key
PREHOOK: type: QUERY
POSTHOOK: query: -- union case: all subqueries are a map-reduce jobs, 3 way union, same input for all sub-queries, followed by reducesink

explain 
  select unionsrc.key, count(1) FROM (select 'tst1' as key, count(1) as value from src s1
                                        UNION  ALL  
                                            select 'tst2' as key, count(1) as value from src s2
                                        UNION ALL
                                            select 'tst3' as key, count(1) as value from src s3) unionsrc group by unionsrc.key
POSTHOOK: type: QUERY
ABSTRACT SYNTAX TREE:
  (TOK_QUERY (TOK_FROM (TOK_SUBQUERY (TOK_UNION (TOK_UNION (TOK_QUERY (TOK_FROM (TOK_TABREF src s1)) (TOK_INSERT (TOK_DESTINATION (TOK_DIR TOK_TMP_FILE)) (TOK_SELECT (TOK_SELEXPR 'tst1' key) (TOK_SELEXPR (TOK_FUNCTION count 1) value)))) (TOK_QUERY (TOK_FROM (TOK_TABREF src s2)) (TOK_INSERT (TOK_DESTINATION (TOK_DIR TOK_TMP_FILE)) (TOK_SELECT (TOK_SELEXPR 'tst2' key) (TOK_SELEXPR (TOK_FUNCTION count 1) value))))) (TOK_QUERY (TOK_FROM (TOK_TABREF src s3)) (TOK_INSERT (TOK_DESTINATION (TOK_DIR TOK_TMP_FILE)) (TOK_SELECT (TOK_SELEXPR 'tst3' key) (TOK_SELEXPR (TOK_FUNCTION count 1) value))))) unionsrc)) (TOK_INSERT (TOK_DESTINATION (TOK_DIR TOK_TMP_FILE)) (TOK_SELECT (TOK_SELEXPR (. (TOK_TABLE_OR_COL unionsrc) key)) (TOK_SELEXPR (TOK_FUNCTION count 1))) (TOK_GROUPBY (. (TOK_TABLE_OR_COL unionsrc) key))))

STAGE DEPENDENCIES:
  Stage-1 is a root stage
  Stage-2 depends on stages: Stage-1, Stage-3, Stage-4
  Stage-3 is a root stage
  Stage-4 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
              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: 'tst1'
                  type: string
                  expr: _col0
                  type: bigint
            outputColumnNames: _col0, _col1
            File Output Operator
              compressed: false
              GlobalTableId: 0
              table:
                  input format: org.apache.hadoop.mapred.SequenceFileInputFormat
                  output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat

  Stage: Stage-2
    Map Reduce
      Alias -> Map Operator Tree:
        file:/data/users/heyongqiang/hive-trunk/.ptest_2/build/ql/tmp/1097598026/10002 
          Union
            Select Operator
              expressions:
                    expr: _col0
                    type: string
              outputColumnNames: _col0
              Group By Operator
                aggregations:
                      expr: count(1)
                bucketGroup: false
                keys:
                      expr: _col0
                      type: string
                mode: hash
                outputColumnNames: _col0, _col1
                Reduce Output Operator
                  key expressions:
                        expr: _col0
                        type: string
                  sort order: +
                  Map-reduce partition columns:
                        expr: _col0
                        type: string
                  tag: -1
                  value expressions:
                        expr: _col1
                        type: bigint
        file:/data/users/heyongqiang/hive-trunk/.ptest_2/build/ql/tmp/1097598026/10003 
          Union
            Select Operator
              expressions:
                    expr: _col0
                    type: string
              outputColumnNames: _col0
              Group By Operator
                aggregations:
                      expr: count(1)
                bucketGroup: false
                keys:
                      expr: _col0
                      type: string
                mode: hash
                outputColumnNames: _col0, _col1
                Reduce Output Operator
                  key expressions:
                        expr: _col0
                        type: string
                  sort order: +
                  Map-reduce partition columns:
                        expr: _col0
                        type: string
                  tag: -1
                  value expressions:
                        expr: _col1
                        type: bigint
        file:/data/users/heyongqiang/hive-trunk/.ptest_2/build/ql/tmp/1097598026/10004 
          Union
            Select Operator
              expressions:
                    expr: _col0
                    type: string
              outputColumnNames: _col0
              Group By Operator
                aggregations:
                      expr: count(1)
                bucketGroup: false
                keys:
                      expr: _col0
                      type: string
                mode: hash
                outputColumnNames: _col0, _col1
                Reduce Output Operator
                  key expressions:
                        expr: _col0
                        type: string
                  sort order: +
                  Map-reduce partition columns:
                        expr: _col0
                        type: string
                  tag: -1
                  value expressions:
                        expr: _col1
                        type: bigint
      Reduce Operator Tree:
        Group By Operator
          aggregations:
                expr: count(VALUE._col0)
          bucketGroup: false
          keys:
                expr: KEY._col0
                type: string
          mode: mergepartial
          outputColumnNames: _col0, _col1
          Select Operator
            expressions:
                  expr: _col0
                  type: string
                  expr: _col1
                  type: bigint
            outputColumnNames: _col0, _col1
            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-3
    Map Reduce
      Alias -> Map Operator Tree:
        null-subquery1-subquery2:unionsrc-subquery1-subquery2:s2 
          TableScan
            alias: s2
            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: 'tst2'
                  type: string
                  expr: _col0
                  type: bigint
            outputColumnNames: _col0, _col1
            File Output Operator
              compressed: false
              GlobalTableId: 0
              table:
                  input format: org.apache.hadoop.mapred.SequenceFileInputFormat
                  output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat

  Stage: Stage-4
    Map Reduce
      Alias -> Map Operator Tree:
        null-subquery2:unionsrc-subquery2:s3 
          TableScan
            alias: s3
            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: 'tst3'
                  type: string
                  expr: _col0
                  type: bigint
            outputColumnNames: _col0, _col1
            File Output Operator
              compressed: false
              GlobalTableId: 0
              table:
                  input format: org.apache.hadoop.mapred.SequenceFileInputFormat
                  output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat

  Stage: Stage-0
    Fetch Operator
      limit: -1


PREHOOK: query: select unionsrc.key, count(1) FROM (select 'tst1' as key, count(1) as value from src s1
                                        UNION  ALL  
                                            select 'tst2' as key, count(1) as value from src s2
                                        UNION ALL
                                            select 'tst3' as key, count(1) as value from src s3) unionsrc group by unionsrc.key
PREHOOK: type: QUERY
PREHOOK: Input: default@src
PREHOOK: Output: file:/data/users/heyongqiang/hive-trunk/.ptest_2/build/ql/tmp/1882920278/10000
POSTHOOK: query: select unionsrc.key, count(1) FROM (select 'tst1' as key, count(1) as value from src s1
                                        UNION  ALL  
                                            select 'tst2' as key, count(1) as value from src s2
                                        UNION ALL
                                            select 'tst3' as key, count(1) as value from src s3) unionsrc group by unionsrc.key
POSTHOOK: type: QUERY
POSTHOOK: Input: default@src
POSTHOOK: Output: file:/data/users/heyongqiang/hive-trunk/.ptest_2/build/ql/tmp/1882920278/10000
tst1	1
tst2	1
tst3	1