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GroupingSets Unary Logical Operator

GroupingSets is a spark-sql-LogicalPlan.md#UnaryNode[unary logical operator] that represents SQL's sql/AstBuilder.md#withAggregation[GROUPING SETS] variant of GROUP BY clause.

val q = sql("""
  SELECT customer, year, SUM(sales)
  FROM VALUES ("abc", 2017, 30) AS t1 (customer, year, sales)
  GROUP BY customer, year
  GROUPING SETS ((customer), (year))
  """)
scala> println(q.queryExecution.logical.numberedTreeString)
00 'GroupingSets [ArrayBuffer('customer), ArrayBuffer('year)], ['customer, 'year], ['customer, 'year, unresolvedalias('SUM('sales), None)]
01 +- 'SubqueryAlias t1
02    +- 'UnresolvedInlineTable [customer, year, sales], [List(abc, 2017, 30)]

GroupingSets operator is resolved to an Aggregate logical operator at <>.

scala> println(q.queryExecution.analyzed.numberedTreeString)
00 Aggregate [customer#8, year#9, spark_grouping_id#5], [customer#8, year#9, sum(cast(sales#2 as bigint)) AS sum(sales)#4L]
01 +- Expand [List(customer#0, year#1, sales#2, customer#6, null, 1), List(customer#0, year#1, sales#2, null, year#7, 2)], [customer#0, year#1, sales#2, customer#8, year#9, spark_grouping_id#5]
02    +- Project [customer#0, year#1, sales#2, customer#0 AS customer#6, year#1 AS year#7]
03       +- SubqueryAlias t1
04          +- LocalRelation [customer#0, year#1, sales#2]

NOTE: GroupingSets can only be created using SQL.

NOTE: GroupingSets is not supported on Structured Streaming's spark-sql-LogicalPlan.md#isStreaming[streaming Datasets].

[[resolved]] GroupingSets is never resolved (as it can only be converted to an Aggregate logical operator).

[[output]] The catalyst/QueryPlan.md#output[output schema] of a GroupingSets are exactly the attributes of <>.

=== [[analyzer]] Analysis Phase

GroupingSets operator is resolved at analysis phase in the following logical evaluation rules:

GroupingSets operator is resolved to an Aggregate.md[Aggregate] with Expand.md[Expand] logical operators.

[source, scala]

val spark: SparkSession = ... // using q from the example above val plan = q.queryExecution.logical

scala> println(plan.numberedTreeString) 00 'GroupingSets [ArrayBuffer('customer), ArrayBuffer('year)], ['customer, 'year], ['customer, 'year, unresolvedalias('SUM('sales), None)] 01 +- 'SubqueryAlias t1 02 +- 'UnresolvedInlineTable [customer, year, sales], [List(abc, 2017, 30)]

// Note unresolvedalias for SUM expression // Note UnresolvedInlineTable and SubqueryAlias

// FIXME Show the evaluation rules to get rid of the unresolvable parts

=== [[creating-instance]] Creating GroupingSets Instance

GroupingSets takes the following when created:

  • [[selectedGroupByExprs]] expressions/Expression.md[Expressions] from GROUPING SETS clause
  • [[groupByExprs]] Grouping expressions/Expression.md[expressions] from GROUP BY clause
  • [[child]] Child spark-sql-LogicalPlan.md[logical plan]
  • [[aggregations]] Aggregate expressions/NamedExpression.md[named expressions]

Last update: 2021-05-24
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