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Date: Tue, 9 Aug 2011 00:54:28 +0000 (UTC)
From: "Charles Chen (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
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Subject: [jira] [Updated] (HIVE-1342) Predicate push down get error result
 when sub-queries have the same alias name
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     [ https://issues.apache.org/jira/browse/HIVE-1342?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Charles Chen updated HIVE-1342:
-------------------------------

    Attachment: HIVE-1342v1.patch

> Predicate push down get error result when sub-queries have the same alias name 
> -------------------------------------------------------------------------------
>
>                 Key: HIVE-1342
>                 URL: https://issues.apache.org/jira/browse/HIVE-1342
>             Project: Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.6.0
>            Reporter: Ted Xu
>            Assignee: Ted Xu
>            Priority: Critical
>         Attachments: HIVE-1342v1.patch, cmd.hql, explain, ppd_same_alias_1.patch, ppd_same_alias_2.patch
>
>
> Query is over-optimized by PPD when sub-queries have the same alias name, see the query:
> -------------------------------
> create table if not exists dm_fact_buyer_prd_info_d (
> 		category_id string
> 		,gmv_trade_num  int
> 		,user_id    int
> 		)
> PARTITIONED BY (ds int);
> set hive.optimize.ppd=true;
> set hive.map.aggr=true;
> explain select category_id1,category_id2,assoc_idx
> from (
> 		select 
> 			category_id1
> 			, category_id2
> 			, count(distinct user_id) as assoc_idx
> 		from (
> 			select 
> 				t1.category_id as category_id1
> 				, t2.category_id as category_id2
> 				, t1.user_id
> 			from (
> 				select category_id, user_id
> 				from dm_fact_buyer_prd_info_d
> 				group by category_id, user_id ) t1
> 			join (
> 				select category_id, user_id
> 				from dm_fact_buyer_prd_info_d
> 				group by category_id, user_id ) t2 on t1.user_id=t2.user_id 
> 			) t1
> 			group by category_id1, category_id2 ) t_o
> 			where category_id1 <> category_id2
> 			and assoc_idx > 2;
> -----------------------------
> The query above will fail when execute, throwing exception: "can not cast UDFOpNotEqual(Text, IntWritable) to UDFOpNotEqual(Text, Text)". 
> I explained the query and the execute plan looks really wired ( only Stage-1, see the highlighted predicate):
> -------------------------------
> Stage: Stage-1
>     Map Reduce
>       Alias -> Map Operator Tree:
>         t_o:t1:t1:dm_fact_buyer_prd_info_d 
>           TableScan
>             alias: dm_fact_buyer_prd_info_d
>             Filter Operator
>               predicate:
>                   expr: *(category_id <> user_id)*
>                   type: boolean
>               Select Operator
>                 expressions:
>                       expr: category_id
>                       type: string
>                       expr: user_id
>                       type: bigint
>                 outputColumnNames: category_id, user_id
>                 Group By Operator
>                   keys:
>                         expr: category_id
>                         type: string
>                         expr: user_id
>                         type: bigint
>                   mode: hash
>                   outputColumnNames: _col0, _col1
>                   Reduce Output Operator
>                     key expressions:
>                           expr: _col0
>                           type: string
>                           expr: _col1
>                           type: bigint
>                     sort order: ++
>                     Map-reduce partition columns:
>                           expr: _col0
>                           type: string
>                           expr: _col1
>                           type: bigint
>                     tag: -1
>       Reduce Operator Tree:
>         Group By Operator
>           keys:
>                 expr: KEY._col0
>                 type: string
>                 expr: KEY._col1
>                 type: bigint
>           mode: mergepartial
>           outputColumnNames: _col0, _col1
>           Select Operator
>             expressions:
>                   expr: _col0
>                   type: string
>                   expr: _col1
>                   type: bigint
>             outputColumnNames: _col0, _col1
>             File Output Operator
>               compressed: true
>               GlobalTableId: 0
>               table:
>                   input format: org.apache.hadoop.mapred.SequenceFileInputFormat
>                   output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
>  ----------------------------------
> If disabling predicate push down (set hive.optimize.ppd=true), the error is gone; I tried disabling map side aggregate, the error is gone,too. 
> *Changing the alias of subquery 't1' (either the inner one or the join result), the bug disappears, too.*

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