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ResolveRelations Logical Resolution Rule

ResolveRelations is a logical resolution rule that the logical query plan analyzer uses to <> (in a logical query plan), i.e.

  • Resolves[UnresolvedRelation] logical operators (in[InsertIntoTable] operators)

  • Other uses of UnresolvedRelation

ResolveRelations is a Catalyst rule for transforming logical plans, i.e. Rule[LogicalPlan].

ResolveRelations is part of Resolution fixed-point batch of rules.


// Example: InsertIntoTable with UnresolvedRelation
import org.apache.spark.sql.catalyst.dsl.plans._
val plan = table("t1").insertInto(tableName = "t2", overwrite = true)
scala> println(plan.numberedTreeString)
00 'InsertIntoTable 'UnresolvedRelation `t2`, true, false
01 +- 'UnresolvedRelation `t1`

// Register the tables so the following resolution works
sql("CREATE TABLE IF NOT EXISTS t1(id long)")
sql("CREATE TABLE IF NOT EXISTS t2(id long)")

// ResolveRelations is a Scala object of the Analyzer class
// We need an instance of the Analyzer class to access it
import spark.sessionState.analyzer.ResolveRelations
val resolvedPlan = ResolveRelations(plan)
scala> println(resolvedPlan.numberedTreeString)
00 'InsertIntoTable 'UnresolvedRelation `t2`, true, false
01 +- 'SubqueryAlias t1
02    +- 'UnresolvedCatalogRelation `default`.`t1`,

// Example: Other uses of UnresolvedRelation
// Use a temporary view
val v1 = spark.range(1).createOrReplaceTempView("v1")
scala> spark.catalog.listTables.filter($"name" === "v1").show
|  v1|    null|       null|TEMPORARY|       true|

import org.apache.spark.sql.catalyst.dsl.expressions._
val plan = table("v1").select(star())
scala> println(plan.numberedTreeString)
00 'Project [*]
01 +- 'UnresolvedRelation `v1`

val resolvedPlan = ResolveRelations(plan)
scala> println(resolvedPlan.numberedTreeString)
00 'Project [*]
01 +- SubqueryAlias v1
02    +- Range (0, 1, step=1, splits=Some(8))

// Example
import org.apache.spark.sql.catalyst.dsl.plans._
val plan = table(db = "db1", ref = "t1")
scala> println(plan.numberedTreeString)
00 'UnresolvedRelation `db1`.`t1`

// Register the database so the following resolution works

val resolvedPlan = ResolveRelations(plan)
scala> println(resolvedPlan.numberedTreeString)
00 'SubqueryAlias t1
01 +- 'UnresolvedCatalogRelation `db1`.`t1`,

=== [[apply]] Applying ResolveRelations to Logical Plan -- apply Method

[source, scala]

apply( plan: LogicalPlan): LogicalPlan

NOTE: apply is part of catalyst/[Rule Contract] to execute a rule on a[logical plan].

For a[InsertIntoTable] logical operator with a[UnresolvedRelation] child operator, apply <> and executes the[EliminateSubqueryAliases] optimization rule.

For a[View] operator, apply substitutes the resolved table for the[InsertIntoTable] operator (that will be no longer a UnresolvedRelation next time the rule is executed). For[View] operator, apply fail analysis with the exception:

Inserting into a view is not allowed. View: [identifier].

For[UnresolvedRelation] logical operators, apply simply <>.

=== [[resolveRelation]] Resolving Relation -- resolveRelation Method

[source, scala]

resolveRelation( plan: LogicalPlan): LogicalPlan


NOTE: resolveRelation is used when ResolveRelations rule is <> (for a[UnresolvedRelation] logical operator).

=== [[isRunningDirectlyOnFiles]] isRunningDirectlyOnFiles Internal Method

[source, scala]

isRunningDirectlyOnFiles(table: TableIdentifier): Boolean

isRunningDirectlyOnFiles is enabled (i.e. true) when all of the following conditions hold:

NOTE: isRunningDirectlyOnFiles is used exclusively when ResolveRelations <> (as a[UnresolvedRelation] leaf logical operator for a table reference).

=== [[lookupTableFromCatalog]] Finding Table in Session-Scoped Catalog of Relational Entities -- lookupTableFromCatalog Internal Method

[source, scala]

lookupTableFromCatalog( u: UnresolvedRelation, defaultDatabase: Option[String] = None): LogicalPlan

lookupTableFromCatalog simply requests SessionCatalog to find the table in relational catalogs.

NOTE: lookupTableFromCatalog requests Analyzer for the current SessionCatalog.

NOTE: The table is described using[TableIdentifier] of the input UnresolvedRelation.

lookupTableFromCatalog fails the analysis phase (by reporting a AnalysisException) when the table or the table's database cannot be found.

NOTE: lookupTableFromCatalog is used when ResolveRelations is <> (for[InsertIntoTable] with UnresolvedRelation operators) or <> (for "standalone"[UnresolvedRelations]).

Last update: 2020-12-28