[jira] [Created] (SPARK-26182) Cost increases when optimizing scalaUDF

["Jiayi Liao (JIRA)" <ji...@apache.org>]

Jiayi Liao created SPARK-26182:
----------------------------------

             Summary: Cost increases when optimizing scalaUDF
                 Key: SPARK-26182
                 URL: https://issues.apache.org/jira/browse/SPARK-26182
             Project: Spark
          Issue Type: Bug
          Components: Optimizer
    Affects Versions: 2.4.0
            Reporter: Jiayi Liao


Let's Assume that we have a udf called splitUDF which outputs a map data.
 The SQL
{code:java}
select
    g['a'], g['b']
from
   ( select splitUDF(x) as g from table) tbl
{code}
will be optimized to the same logical plan of
{code:java}
select splitUDF(x)['a'], splitUDF(x)['b'] from table
{code}
which means that the splitUDF is executed twice instead of once.

The optimization is from CollapseProject. 
 I'm not sure whether this is a bug or not. Please tell me if I was wrong about this.



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