[jira] [Created] (HIVE-21398) Columns which has estimated statistics should not be considered as unique keys

["Zoltan Haindrich (JIRA)" <ji...@apache.org>]

Zoltan Haindrich created HIVE-21398:
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             Summary: Columns which has estimated statistics should not be considered as unique keys
                 Key: HIVE-21398
                 URL: https://issues.apache.org/jira/browse/HIVE-21398
             Project: Hive
          Issue Type: Bug
            Reporter: Zoltan Haindrich
            Assignee: Zoltan Haindrich


Right now for a column to qualify as a unique column it has to meet the criteria: 
{code}
NDV >= numRows
{code}
when numRows is 1 this tends to be true ; but numRows is also 1 in cases when we are kinda operate in the blind - don't know how many row there are - more generatlly: with estimated column statistics.

As a sideeffect of qualifying all columns to be unique; after a few joins all column combinations became unique....so for a join between 3 tables which have (i,j,k) columns; then it will allocate {{i*j*k}} triplets of "unique column triplets".





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