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EliminateView Logical Optimization

EliminateView is a base logical optimization that <>.

EliminateView is part of the Finish Analysis once-executed batch in the standard batches of the Logical Optimizer.

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

[source, scala]

val name = "demo_view" sql(s"CREATE OR REPLACE VIEW $name COMMENT 'demo view' AS VALUES 1,2") assert(spark.catalog.tableExists(name))

val q = spark.table(name)

val analyzedPlan = q.queryExecution.analyzed scala> println(analyzedPlan.numberedTreeString) 00 SubqueryAlias demo_view 01 +- View (default.demo_view, [col1#37]) 02 +- Project [cast(col1#38 as int) AS col1#37] 03 +- LocalRelation [col1#38]

import org.apache.spark.sql.catalyst.analysis.EliminateView val afterEliminateView = EliminateView(analyzedPlan) // Notice no View operator scala> println(afterEliminateView.numberedTreeString) 00 SubqueryAlias demo_view 01 +- Project [cast(col1#38 as int) AS col1#37] 02 +- LocalRelation [col1#38]

// TIP: You may also want to use EliminateSubqueryAliases to eliminate SubqueryAliases

Executing Rule

apply(plan: LogicalPlan): LogicalPlan

apply simply removes (eliminates) <> unary logical operators from the input <> and replaces them with their <> logical operator.

apply throws an AssertionError when the <> of the View operator does not match the <> of the <> logical operator.

assertion failed: The output of the child [output] is different from the view output [output]

NOTE: The assertion should not really happen since AliasViewChild logical analysis rule is executed earlier and takes care of not allowing for such difference in the output schema (by throwing an AnalysisException earlier).

apply is part of the Rule abstraction.


Last update: 2020-11-07