spark技术分享Attribute — Base of Leaf Named Expressions
Attribute is the base of leaf named expressions.
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QueryPlan uses Attributes to build the schema of the query (it represents). |
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package org.apache.spark.sql.catalyst.expressions abstract class Attribute extends ... { // only required properties (vals and methods) that have no implementation // the others follow def withMetadata(newMetadata: Metadata): Attribute def withName(newName: String): Attribute def withNullability(newNullability: Boolean): Attribute def withQualifier(newQualifier: Option[String]): Attribute def newInstance(): Attribute } |
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When requested for references, Attribute gives the reference to itself only.
As a NamedExpression, Attribute gives the reference to itself only when requested for toAttribute.
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As an optimization, Attribute is marked as to not tolerate nulls, and when given a null input produces a null output.
