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View Unary Logical Operator

[[children]] View is a <> with a single <> logical operator.

View is <> exclusively when SessionCatalog is requested to find a relation in the catalogs (e.g. when DescribeTableCommand logical command is <> and the table type is VIEW).

[source, scala]

// Let's create a view first // Using SQL directly to manage views is so much nicer 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 = sql(s"DESC EXTENDED $name")

val allRowsIncluded = 100 scala> q.show(numRows = allRowsIncluded) +--------------------+--------------------+-------+ | col_name| data_type|comment| +--------------------+--------------------+-------+ | col1| int| null| | | | | |# Detailed Table ...| | | | Database| default| | | Table| demo_view| | | Owner| jacek| | | Created Time|Thu Aug 30 08:55:...| | | Last Access|Thu Jan 01 01:00:...| | | Created By| Spark 2.3.1| | | Type| VIEW| | | Comment| demo view| | | View Text| VALUES 1,2| | |View Default Data...| default| | |View Query Output...| [col1]| | | Table Properties|[transient_lastDd...| | | Serde Library|org.apache.hadoop...| | | InputFormat|org.apache.hadoop...| | | OutputFormat|org.apache.hadoop...| | | Storage Properties|[serialization.fo...| | +--------------------+--------------------+-------+

[[newInstance]] View is a MultiInstanceRelation so a <> to appear multiple times in a physical query plan. When requested for a new instance, View <> of the <>.

[[resolved]] View is considered <> only when the <> is.

[[simpleString]] View has the following <>:

View ([identifier], [output])

[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 qe = q.queryExecution

val logicalPlan = qe.logical scala> println(logicalPlan.simpleString) 'UnresolvedRelation demo_view

val analyzedPlan = qe.analyzed scala> println(analyzedPlan.numberedTreeString) 00 SubqueryAlias demo_view 01 +- View (default.demo_view, [col1#33]) 02 +- Project [cast(col1#34 as int) AS col1#33] 03 +- LocalRelation [col1#34]

// Skip SubqueryAlias scala> println(analyzedPlan.children.head.simpleString) View (default.demo_view, [col1#33])

NOTE: View is resolved by ResolveRelationslogical resolution.

NOTE: AliasViewChild logical analysis rule makes sure that the <> of a View matches the output of the <> logical operator.

NOTE: <> logical optimization removes (eliminates) View operators from a logical query plan.

NOTE: <>.

Creating Instance

View takes the following when created: