SortOrder¶

SortOrder is an Expression that represents the following operators in a structured query:

• AstBuilder is requested to parse ORDER BY or SORT BY sort specifications

• Column.asc, Column.asc_nulls_first, Column.asc_nulls_last, Column.desc, Column.desc_nulls_first, and Column.desc_nulls_last high-level operators

SortOrder is also used to specify the output data ordering requirements and the required child ordering of physical operators.

Creating Instance¶

SortOrder takes the following to be created:

• Child Expression
• SortDirection
• NullOrdering
• "Same Order" Expressions

SortDirection¶

NullOrdering¶

Creating SortOrder¶

apply(
  child: Expression,
  direction: SortDirection,
  sameOrderExpressions: Seq[Expression] = Seq.empty): SortOrder

apply creates a SortOrder (with the defaultNullOrdering of the given SortDirection).

apply is created when:

• ResolveCoalesceHints logical analysis rule is executed
• many many others

Catalyst DSL¶

Catalyst DSL defines the following operators to create SortOrders:

• asc (with nulls first)
• asc_nullsLast
• desc (with nulls last)
• desc_nullsFirst

import org.apache.spark.sql.catalyst.dsl.expressions._
val sortNullsLast = 'id.asc_nullsLast

scala> println(sortNullsLast.sql)
`id` ASC NULLS LAST

Unevaluable¶

SortOrder is an Unevaluable expression.