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From paul-rogers <...@git.apache.org>
Subject [GitHub] drill pull request #775: DRILL-5326: Unit tests failures related to the SERV...
Date Tue, 07 Mar 2017 23:42:04 GMT
Github user paul-rogers commented on a diff in the pull request:

    https://github.com/apache/drill/pull/775#discussion_r104809964
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/work/metadata/ServerMetaProvider.java
---
    @@ -76,7 +76,7 @@
           .setReadOnly(false)
           .setGroupBySupport(GroupBySupport.GB_UNRELATED)
           .setLikeEscapeClauseSupported(true)
    -      .setNullCollation(NullCollation.NC_AT_END)
    +      .setNullCollation(NullCollation.NC_HIGH)
    --- End diff --
    
    When sorting in Drill, the detailed sort spec is set in the {{ExternalSort}} operator
definition. This thing is a bit complex. One can control sort order (ASC, DESC) and nulls
position (LOW, HIGH, UNSPECIFIED.)
    
    Data sorts according to ASC, DESC.
    Nulls sort as follows:
    
    HIGH: last if ASC, first if DESC
    LOW: first if ASC, last if DESC
    UNSPECIFIED: always high
    
    If the planner has no way of setting the nulls ordering from a SQL query, then the value
is UNSPECIFIED, which means nulls always sort last as Jinfeng explained.


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