hadoop explain left join 语句在执行计划变成了 Inner Join ，求大神解惑！

在两个sql语句中，第一个是我想要的，但是刚写出来的时候是第二个，第二个sql语句执行计划里的left join变成了inner join，不知所云，希望老师们解答一下!



 hive> explain select t1.device_id,t1.sid, t2.sid 



    > from (select * from playqos_action_detail where curdate='20161101') t1 



    > left join (select * from seek_pause_buffer_action where curdate='20161101' and action='http://wenda.chinahadoop.cn/SeekAction') t2



    > on (t1.sid=t2.sid and t1.device_id=t2.device_id)



    > where t1.device_id='015163005010013'



    > ;



OK



STAGE DEPENDENCIES:



  Stage-1 is a root stage



  Stage-0 depends on stages: Stage-1







STAGE PLANS:



  Stage: Stage-1



    Map Reduce



      Map Operator Tree:



          TableScan



            alias: playqos_action_detail



            Statistics: Num rows: 3568808 Data size: 1137545459 Basic stats: COMPLETE Column stats: NONE



            Filter Operator



              predicate: (device_id = '015163005010013') (type: boolean)



              Statistics: Num rows: 1784404 Data size: 568772729 Basic stats: COMPLETE Column stats: NONE



              Select Operator



                expressions: '015163005010013' (type: string), sid (type: string)



                outputColumnNames: _col0, _col1



                Statistics: Num rows: 1784404 Data size: 568772729 Basic stats: COMPLETE Column stats: NONE



                Reduce Output Operator



                  key expressions: _col1 (type: string), _col0 (type: string)



                  sort order: ++



                  Map-reduce partition columns: _col1 (type: string), _col0 (type: string)



                  Statistics: Num rows: 1784404 Data size: 568772729 Basic stats: COMPLETE Column stats: NONE



          TableScan



            alias: seek_pause_buffer_action



            Statistics: Num rows: 1296952 Data size: 71839667 Basic stats: COMPLETE Column stats: NONE



            Filter Operator



              predicate: ((action = 'SeekAction') and (device_id = '015163005010013')) (type: boolean)



              Statistics: Num rows: 324238 Data size: 17959916 Basic stats: COMPLETE Column stats: NONE



              Select Operator



                expressions: '015163005010013' (type: string), sid (type: string)



                outputColumnNames: _col0, _col1



                Statistics: Num rows: 324238 Data size: 17959916 Basic stats: COMPLETE Column stats: NONE



                Reduce Output Operator



                  key expressions: _col1 (type: string), _col0 (type: string)



                  sort order: ++



                  Map-reduce partition columns: _col1 (type: string), _col0 (type: string)



                  Statistics: Num rows: 324238 Data size: 17959916 Basic stats: COMPLETE Column stats: NONE



      Reduce Operator Tree:



        Join Operator



          condition map:



               Left Outer Join0 to 1



          keys:



            0 _col1 (type: string), _col0 (type: string)



            1 _col1 (type: string), _col0 (type: string)



          outputColumnNames: _col0, _col1, _col3



          Statistics: Num rows: 1962844 Data size: 625650015 Basic stats: COMPLETE Column stats: NONE



          Select Operator



            expressions: _col0 (type: string), _col1 (type: string), _col3 (type: string)



            outputColumnNames: _col0, _col1, _col2



            Statistics: Num rows: 1962844 Data size: 625650015 Basic stats: COMPLETE Column stats: NONE



            File Output Operator



              compressed: false



              Statistics: Num rows: 1962844 Data size: 625650015 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







  Stage: Stage-0



    Fetch Operator



      limit: -1



      Processor Tree:



        ListSink







Time taken: 0.16 seconds, Fetched: 65 row(s)



hive> explain select a.device_id,a.sid, 



    > (case when b.device_id is NULL then NULL else b.device_id end), 



    > (case when b.sid is NULL then NULL else b.sid end)



    > from playqos_action_detail a left join seek_pause_buffer_action b on   a.sid=b.sid 



    > where a.curdate='20161101'  and a.device_id='015163005010013'



    > and b.curdate='20161101' and action='http://wenda.chinahadoop.cn/SeekAction';



OK



STAGE DEPENDENCIES:



  Stage-1 is a root stage



  Stage-0 depends on stages: Stage-1







STAGE PLANS:



  Stage: Stage-1



    Map Reduce



      Map Operator Tree:



          TableScan



            alias: a



            Statistics: Num rows: 3568808 Data size: 1137545459 Basic stats: COMPLETE Column stats: NONE



            Filter Operator



              predicate: ((device_id = '015163005010013') and sid is not null) (type: boolean)



              Statistics: Num rows: 1784404 Data size: 568772729 Basic stats: COMPLETE Column stats: NONE



              Select Operator



                expressions: sid (type: string)



                outputColumnNames: _col1



                Statistics: Num rows: 1784404 Data size: 568772729 Basic stats: COMPLETE Column stats: NONE



                Reduce Output Operator



                  key expressions: _col1 (type: string)



                  sort order: +



                  Map-reduce partition columns: _col1 (type: string)



                  Statistics: Num rows: 1784404 Data size: 568772729 Basic stats: COMPLETE Column stats: NONE



          TableScan



            alias: b



            Statistics: Num rows: 1296952 Data size: 71839667 Basic stats: COMPLETE Column stats: NONE



            Filter Operator



              predicate: ((action = 'SeekAction') and sid is not null) (type: boolean)



              Statistics: Num rows: 648476 Data size: 35919833 Basic stats: COMPLETE Column stats: NONE



              Select Operator



                expressions: device_id (type: string), sid (type: string)



                outputColumnNames: _col0, _col1



                Statistics: Num rows: 648476 Data size: 35919833 Basic stats: COMPLETE Column stats: NONE



                Reduce Output Operator



                  key expressions: _col1 (type: string)



                  sort order: +



                  Map-reduce partition columns: _col1 (type: string)



                  Statistics: Num rows: 648476 Data size: 35919833 Basic stats: COMPLETE Column stats: NONE



                  value expressions: _col0 (type: string)



      Reduce Operator Tree:



        Join Operator



          condition map:



               Inner Join 0 to 1



          keys:



            0 _col1 (type: string)



            1 _col1 (type: string)



          outputColumnNames: _col1, _col3, _col4



          Statistics: Num rows: 1962844 Data size: 625650015 Basic stats: COMPLETE Column stats: NONE



          Select Operator



            expressions: '015163005010013' (type: string), _col1 (type: string), CASE WHEN (_col3 is null) THEN (null) ELSE (_col3) END (type: string), CASE WHEN (_col4 is null) THEN (null) ELSE (_col4) END (type: string)



            outputColumnNames: _col0, _col1, _col2, _col3



            Statistics: Num rows: 1962844 Data size: 625650015 Basic stats: COMPLETE Column stats: NONE



            File Output Operator



              compressed: false



              Statistics: Num rows: 1962844 Data size: 625650015 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







  Stage: Stage-0



    Fetch Operator



      limit: -1



      Processor Tree:



        ListSink







Time taken: 0.139 seconds, Fetched: 66 row(s)



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