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DecimalAggregates Logical Optimization

DecimalAggregates is a base logical optimization that <> Sum and Average aggregate functions on fixed-precision DecimalType values to use UnscaledValue (unscaled Long) values in spark-sql-Expression-WindowExpression.md[WindowExpression] and AggregateExpression expressions.

DecimalAggregates is part of the Decimal Optimizations fixed-point batch in the standard batches of the Logical Optimizer.

DecimalAggregates is simply a <> for transforming <>, i.e. Rule[LogicalPlan].

[TIP]

Import DecimalAggregates and apply the rule directly on your structured queries to learn how the rule works.

[source, scala]

import org.apache.spark.sql.catalyst.optimizer.DecimalAggregates val da = DecimalAggregates(spark.sessionState.conf)

// Build analyzed logical plan // with sum aggregate function and Decimal field import org.apache.spark.sql.types.DecimalType val query = spark.range(5).select(sum($"id" cast DecimalType(1,0)) as "sum") scala> val plan = query.queryExecution.analyzed plan: org.apache.spark.sql.catalyst.plans.logical.LogicalPlan = Aggregate [sum(cast(id#91L as decimal(1,0))) AS sum#95] +- Range (0, 5, step=1, splits=Some(8))

// Apply DecimalAggregates rule // Note MakeDecimal and UnscaledValue operators scala> da.apply(plan) res27: org.apache.spark.sql.catalyst.plans.logical.LogicalPlan = Aggregate [MakeDecimal(sum(UnscaledValue(cast(id#91L as decimal(1,0)))),11,0) AS sum#95] +- Range (0, 5, step=1, splits=Some(8))


====

=== [[example-sum-decimal]] Example: sum Aggregate Function on Decimal with Precision Smaller Than 9

[source, scala]

// sum aggregate with Decimal field with precision <= 8 val q = "SELECT sum(cast(id AS DECIMAL(5,0))) FROM range(1)"

scala> sql(q).explain(true) == Parsed Logical Plan == 'Project [unresolvedalias('sum(cast('id as decimal(5,0))), None)] +- 'UnresolvedTableValuedFunction range, [1]

== Analyzed Logical Plan == sum(CAST(id AS DECIMAL(5,0))): decimal(15,0) Aggregate [sum(cast(id#104L as decimal(5,0))) AS sum(CAST(id AS DECIMAL(5,0)))#106] +- Range (0, 1, step=1, splits=None)

== Optimized Logical Plan == Aggregate [MakeDecimal(sum(UnscaledValue(cast(id#104L as decimal(5,0)))),15,0) AS sum(CAST(id AS DECIMAL(5,0)))#106] +- Range (0, 1, step=1, splits=None)

== Physical Plan == *HashAggregate(keys=[], functions=[sum(UnscaledValue(cast(id#104L as decimal(5,0))))], output=[sum(CAST(id AS DECIMAL(5,0)))#106]) +- Exchange SinglePartition +- *HashAggregate(keys=[], functions=[partial_sum(UnscaledValue(cast(id#104L as decimal(5,0))))], output=[sum#108L]) +- *Range (0, 1, step=1, splits=None)


=== [[example-avg-decimal]] Example: avg Aggregate Function on Decimal with Precision Smaller Than 12

[source, scala]

// avg aggregate with Decimal field with precision <= 11 val q = "SELECT avg(cast(id AS DECIMAL(10,0))) FROM range(1)"

scala> val q = "SELECT avg(cast(id AS DECIMAL(10,0))) FROM range(1)" q: String = SELECT avg(cast(id AS DECIMAL(10,0))) FROM range(1)

scala> sql(q).explain(true) == Parsed Logical Plan == 'Project [unresolvedalias('avg(cast('id as decimal(10,0))), None)] +- 'UnresolvedTableValuedFunction range, [1]

== Analyzed Logical Plan == avg(CAST(id AS DECIMAL(10,0))): decimal(14,4) Aggregate [avg(cast(id#115L as decimal(10,0))) AS avg(CAST(id AS DECIMAL(10,0)))#117] +- Range (0, 1, step=1, splits=None)

== Optimized Logical Plan == Aggregate [cast((avg(UnscaledValue(cast(id#115L as decimal(10,0)))) / 1.0) as decimal(14,4)) AS avg(CAST(id AS DECIMAL(10,0)))#117] +- Range (0, 1, step=1, splits=None)

== Physical Plan == *HashAggregate(keys=[], functions=[avg(UnscaledValue(cast(id#115L as decimal(10,0))))], output=[avg(CAST(id AS DECIMAL(10,0)))#117]) +- Exchange SinglePartition +- *HashAggregate(keys=[], functions=[partial_avg(UnscaledValue(cast(id#115L as decimal(10,0))))], output=[sum#120, count#121L]) +- *Range (0, 1, step=1, splits=None)


Executing Rule

apply(plan: LogicalPlan): LogicalPlan

apply...FIXME

apply is part of the Rule abstraction.


Last update: 2020-08-05