EnricoMi commented on code in PR #37407:
URL: https://github.com/apache/spark/pull/37407#discussion_r970561575
##########
sql/catalyst/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBaseParser.g4:
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@@ -618,6 +618,46 @@ pivotValue
: expression (AS? identifier)?
;
+unpivotClause
+ : UNPIVOT nullOperator=unpivotNullClause? LEFT_PAREN
+ operator=unpivotOperator
+ RIGHT_PAREN (AS? identifier)?
+ ;
+
+unpivotNullClause
+ : (INCLUDE | EXCLUDE) NULLS
+ ;
+
+unpivotOperator
+ : (unpivotSingleValueColumnClause | unpivotMultiValueColumnClause)
+ ;
+
+unpivotSingleValueColumnClause
+ : unpivotValueColumn FOR unpivotNameColumn IN LEFT_PAREN
unpivotColumns+=unpivotColumn (COMMA unpivotColumns+=unpivotColumn)* RIGHT_PAREN
+ ;
+
+unpivotMultiValueColumnClause
+ : LEFT_PAREN unpivotValueColumns+=unpivotValueColumn (COMMA
unpivotValueColumns+=unpivotValueColumn)* RIGHT_PAREN
+ FOR unpivotNameColumn
+ IN LEFT_PAREN unpivotColumnSets+=unpivotColumnSet (COMMA
unpivotColumnSets+=unpivotColumnSet)* RIGHT_PAREN
+ ;
+
+unpivotColumnSet
+ : LEFT_PAREN unpivotColumns+=unpivotColumn (COMMA
unpivotColumns+=unpivotColumn)* RIGHT_PAREN (AS? identifier)?
Review Comment:
Without an alias result contains string representation of the column name
tuples:
https://github.com/apache/spark/pull/37407/files#diff-f306d1dfcd20c4cdcdb5d631416ee9d92bf6893422b0a9683ca4493d7215e5e8R199-R212
```
-- !query
SELECT * FROM courseEarningsAndSales
UNPIVOT (
(earnings, sales) FOR year IN ((earnings2012, sales2012), (earnings2013,
sales2013), (earnings2014, sales2014))
)
-- !query schema
struct<course:string,year:string,earnings:int,sales:int>
-- !query output
Java (`earnings2012`,`sales2012`) 20000 1
Java (`earnings2013`,`sales2013`) 30000 2
Java (`earnings2014`,`sales2014`) NULL NULL
dotNET (`earnings2012`,`sales2012`) 15000 2
dotNET (`earnings2013`,`sales2013`) 48000 1
dotNET (`earnings2014`,`sales2014`) 22500 1
```
If users are happy with that, why forcing an alias?
This is optional in
[BigQuery](https://cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax#unpivot_operator)
as well, the other SQL flavours mentioned in the PR description are not
specific in that matter.
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