[HIVE-582] "SELECT count(1) as cnt from src x" not working for column pruning

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.4.0
• Hadoop Flags: Reviewed
• Assignee: He Yongqiang
• Reporter: He Yongqiang
• Created: 25/Jun/09 09:36
• Updated: 17/Dec/11 00:07
• Resolved: 30/Jun/09 00:54

Description

The query "SELECT count(1) as cnt from src x" has some problems, even though nullgroup*.q passed in tests.
Will check and solve it in this jira.
A wrong plan sometimes can be generated due to some unknow factor:
Wrong plan:

STAGE PLANS:
  Stage: Stage-1
    Map Reduce
      Alias -> Map Operator Tree:
        x 
            Select Operator
              Reduce Output Operator
                sort order: 
                tag: -1
      Reduce Operator Tree:
        Group By Operator
          aggregations:
                expr: count(VALUE._col0)
          mode: complete
          Select Operator
            expressions:
                  expr: _col0
                  type: bigint
            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

Without unknow factor, correct plan can be generated:

STAGE PLANS:
  Stage: Stage-1
    Map Reduce
      Alias -> Map Operator Tree:
        x 
            Select Operator
              Group By Operator
                aggregations:
                      expr: count(1)
                mode: hash
                Reduce Output Operator
                  sort order: 
                  tag: -1
                  value expressions:
                        expr: _col0
                        type: bigint
      Reduce Operator Tree:
        Group By Operator
          aggregations:
                expr: count(VALUE._col0)
          mode: mergepartial
          Select Operator
            expressions:
                  expr: _col0
                  type: bigint
            File Output Operator
              compressed: false
              GlobalTableId: 0
              table:
                  input format: org.apache.hadoop.mapred.TextInputFormat
                  output format: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat