Hanumath Rao Maduri created DRILL-6312:
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             Summary: Enable pushing of cast expressions to the scanner for 
better schema discovery.
                 Key: DRILL-6312
                 URL: https://issues.apache.org/jira/browse/DRILL-6312
             Project: Apache Drill
          Issue Type: Bug
          Components: Execution - Relational Operators, Query Planning & 
Optimization
    Affects Versions: 1.13.0
            Reporter: Hanumath Rao Maduri


Drill is a schema less engine which tries to infer the schema from disparate 
sources at the read time. Currently the scanners infer the schema for each 
batch depending upon the data for that column in the corresponding batch. This 
solves many uses cases but can error out when the data is too different between 
batches like int and array[int] etc... (There are other cases as well but just 
to give one example).

There is also a mechanism to create a view by type casting the columns to 
appropriate type. This solves issues in some cases but fails in many other 
cases. This is due to the fact that cast expression is not being pushed down to 
the scanner but staying at the project or filter etc operators up the query 
plan.

This JIRA is to fix this by propagating the type information embedded in the 
cast function to the scanners so that scanners can cast the incoming data 
appropriately.





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