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  1. Apache Drill
  2. DRILL-6734

Unable to find value vector of path `EXPR$0`, returning null instance.

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Details

    • Bug
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • 1.14.0
    • 1.16.0
    • Storage - JDBC
    • Apache Drill version 1.14.0 running on CentOS 7.0.1406.
      MySQL version 5.5.43 running on CentOS 6.4.
      MySQL connector/j version 5.1.44.

    Description

      Expressions in a query against JDBC without alias returns null as their value.

      I was trying to run this sample query to retrieve count of a MySQL table connected to Drill through the RDBMS storage plugin:

      select count(*) from ngmysql.information_schema.`PROCESSLIST`
      

      which returns

      EXPR$0       
      -------------
      <null>       
      

      and you could find this warning from the log:

      Unable to find value vector of path `EXPR$0`, returning null instance.

      But it works fine if you give an alias to the expression like this:

      select count(*) as num from ngmysql.information_schema.`PROCESSLIST`;
      

      which would end up giving this:

      num                   
      ----------------------
      16                    
      

      Here's the portion of logs regarding the sample query:

      2018-09-07 21:44:52,709 [246d0eaa-f8e6-9536-af0c-1df3932cce9f:foreman] INFO  o.a.drill.exec.work.foreman.Foreman - Query text for query id 246d0eaa-f8e6-9536-af0c-1df3932cce9f: select count(*) from ngmysql.information_schema.`PROCESSLIST`
      2018-09-07 21:44:52,752 [246d0eaa-f8e6-9536-af0c-1df3932cce9f:frag:0:0] INFO  o.a.d.e.w.fragment.FragmentExecutor - 246d0eaa-f8e6-9536-af0c-1df3932cce9f:0:0: State change requested AWAITING_ALLOCATION --> RUNNING
      2018-09-07 21:44:52,753 [246d0eaa-f8e6-9536-af0c-1df3932cce9f:frag:0:0] INFO  o.a.d.e.w.f.FragmentStatusReporter - 246d0eaa-f8e6-9536-af0c-1df3932cce9f:0:0: State to report: RUNNING
      2018-09-07 21:44:52,756 [246d0eaa-f8e6-9536-af0c-1df3932cce9f:frag:0:0] WARN  o.a.d.e.e.ExpressionTreeMaterializer - Unable to find value vector of path `EXPR$0`, returning null instance.
      2018-09-07 21:44:52,759 [246d0eaa-f8e6-9536-af0c-1df3932cce9f:frag:0:0] INFO  o.a.d.e.w.fragment.FragmentExecutor - 246d0eaa-f8e6-9536-af0c-1df3932cce9f:0:0: State change requested RUNNING --> FINISHED
      2018-09-07 21:44:52,760 [246d0eaa-f8e6-9536-af0c-1df3932cce9f:frag:0:0] INFO  o.a.d.e.w.f.FragmentStatusReporter - 246d0eaa-f8e6-9536-af0c-1df3932cce9f:0:0: State to report: FINISHED
      

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              volodymyr Vova Vysotskyi
              appler Cheolgoo Kang
              Vitalii Diravka Vitalii Diravka
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                Created:
                Updated:
                Resolved: