[jira] [Created] (SPARK-17271) Planner adds un-necessary Sort even if child ordering is semantically same as required ordering

["Tejas Patil (JIRA)" <ji...@apache.org>]

Tejas Patil created SPARK-17271:
-----------------------------------

             Summary: Planner adds un-necessary Sort even if child ordering is semantically same as required ordering
                 Key: SPARK-17271
                 URL: https://issues.apache.org/jira/browse/SPARK-17271
             Project: Spark
          Issue Type: Bug
          Components: SQL
    Affects Versions: 2.0.0, 1.6.2
            Reporter: Tejas Patil


Found a case when the planner is adding un-needed SORT operation due to bug in the way comparison for `SortOrder` is done at https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/EnsureRequirements.scala#L253

`SortOrder` needs to be compared semantically because `Expression` within two `SortOrder` can be "semantically equal" but not literally equal objects.

eg. In case of `sql("SELECT * FROM table1 a JOIN table2 b ON a.col1=b.col1")`

Expression in required SortOrder:

```
      AttributeReference(
        name = "col1",
        dataType = LongType,
        nullable = false
      ) (exprId = exprId,
        qualifier = Some("a")
      )
```

Expression in child SortOrder:

```
      AttributeReference(
        name = "col1",
        dataType = LongType,
        nullable = false
      ) (exprId = exprId)
```

Notice that the output column has a qualifier but the child attribute does not but the inherent expression is the same and hence in this case we can say that the child satisfies the required sort order.



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