Ratandeep Ratti created HIVE-14351:
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             Summary: Minor improvement in genUnionPlan method
                 Key: HIVE-14351
                 URL: https://issues.apache.org/jira/browse/HIVE-14351
             Project: Hive
          Issue Type: Improvement
    Affects Versions: 2.1.0
            Reporter: Ratandeep Ratti
            Assignee: Ratandeep Ratti


{{org.apache.hadoop.hive.ql.parse.SemanticAnalyzer#genUnionPlan}} method can 
trip new users reading the code.

Specifically on line 8979
{code}
HashMap<String, ColumnInfo> leftmap = leftRR.getFieldMap(leftalias);
HashMap<String, ColumnInfo> rightmap = rightRR.getFieldMap(rightalias);
{code}

These column maps are actually LinkedHashMaps and the code relies on this fact  
when iterating the two union branches in order.  

This was not clear immediately and  left me wondering how is it that traversal 
order is consistent.

I've updated the code with this simple fix.









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