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## What changes were proposed in this pull request? Add SQL support for Pivot according to Pivot grammar defined by Oracle (https://docs.oracle.com/database/121/SQLRF/img_text/pivot_clause.htm) with some simplifications, based on our existing functionality and limitations for Pivot at the backend: 1. For pivot_for_clause (https://docs.oracle.com/database/121/SQLRF/img_text/pivot_for_clause.htm), the column list form is not supported, which means the pivot column can only be one single column. 2. For pivot_in_clause (https://docs.oracle.com/database/121/SQLRF/img_text/pivot_in_clause.htm), the sub-query form and "ANY" is not supported (this is only supported by Oracle for XML anyway). 3. For pivot_in_clause, aliases for the constant values are not supported. The code changes are: 1. Add parser support for Pivot. Note that according to https://docs.oracle.com/database/121/SQLRF/statements_10002.htm#i2076542, Pivot cannot be used together with lateral views in the from clause. This restriction has been implemented in the Parser rule. 2. Infer group-by expressions: group-by expressions are not explicitly specified in SQL Pivot clause and need to be deduced based on this rule: https://docs.oracle.com/database/121/SQLRF/statements_10002.htm#CHDFAFIE, so we have to post-fix it at query analysis stage. 3. Override Pivot.resolved as "false": for the reason mentioned in [2] and the fact that output attributes change after Pivot being replaced by Project or Aggregate, we avoid resolving parent references until after Pivot has been resolved and replaced. 4. Verify aggregate expressions: only aggregate expressions with or without aliases can appear in the first part of the Pivot clause, and this check is performed as analysis stage. ## How was this patch tested? A new test suite PivotSuite is added. Author: maryannxue <maryann.xue@gmail.com> Closes #21187 from maryannxue/spark-24035. |
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