Skip to content

Sort Unary Logical Operator

Sort is a <> that represents the following in a logical plan:

  • ORDER BY, SORT BY, SORT BY ... DISTRIBUTE BY and CLUSTER BY clauses (when AstBuilder is requested to <>)

  • <>, <> and <> operators

[source, scala]

// Using the feature of ordinal literal val ids = Seq(1,3,2).toDF("id").sort(lit(1)) val logicalPlan = ids.queryExecution.logical scala> println(logicalPlan.numberedTreeString) 00 Sort [1 ASC NULLS FIRST], true 01 +- AnalysisBarrier 02 +- Project [value#22 AS id#24] 03 +- LocalRelation [value#22]

import org.apache.spark.sql.catalyst.plans.logical.Sort val sortOp = logicalPlan.collect { case s: Sort => s }.head scala> println(sortOp.numberedTreeString) 00 Sort [1 ASC NULLS FIRST], true 01 +- AnalysisBarrier 02 +- Project [value#22 AS id#24] 03 +- LocalRelation [value#22]

[source, scala]

val nums = Seq((0, "zero"), (1, "one")).toDF("id", "name") // Creates a Sort logical operator: // - descending sort direction for id column (specified explicitly) // - name column is wrapped with ascending sort direction val numsOrdered = nums.sort('id.desc, 'name) val logicalPlan = numsOrdered.queryExecution.logical scala> println(logicalPlan.numberedTreeString) 00 'Sort ['id DESC NULLS LAST, 'name ASC NULLS FIRST], true 01 +- Project [_1#11 AS id#14, _2#12 AS name#15] 02 +- LocalRelation [_1#11, _2#12]

[[creating-instance]] Sort takes the following when created:

  • [[order]] <> ordering expressions
  • [[global]] global flag for global (true) or partition-only (false) sorting
  • [[child]] Child <>

[[output]] The <> of a Sort operator is the output of the <> logical operator.

[[maxRows]] The <> of a Sort operator is the maxRows of the <> logical operator.

[[catalyst-dsl]] TIP: Use <> or <> operators from the Catalyst DSL to create a Sort logical operator, e.g. for testing or Spark SQL internals exploration.

NOTE: Sorting is supported for columns of orderable type only (which is enforced at analysis when CheckAnalysis is requested to <>).

NOTE: Sort logical operator is resolved to <> unary physical operator when BasicOperators execution planning strategy is executed.

=== [[orderBy]][[sortBy]] Catalyst DSL -- orderBy and sortBy Operators

[source, scala]

orderBy(sortExprs: SortOrder*): LogicalPlan sortBy(sortExprs: SortOrder*): LogicalPlan

orderBy and sortBy <> a Sort logical operator with the <> flag on and off, respectively.

[source, scala]

import org.apache.spark.sql.catalyst.dsl.plans._ val t1 = table("t1")

import org.apache.spark.sql.catalyst.dsl.expressions._ val globalSortById = t1.orderBy('id.asc_nullsLast)

// Note true for the global flag scala> println(globalSortById.numberedTreeString) 00 'Sort ['id ASC NULLS LAST], true 01 +- 'UnresolvedRelation t1

// Note false for the global flag val partitionOnlySortById = t1.sortBy('id.asc_nullsLast) scala> println(partitionOnlySortById.numberedTreeString) 00 'Sort ['id ASC NULLS LAST], false 01 +- 'UnresolvedRelation t1

Last update: 2020-11-16