spark技术分享GetCurrentDatabase Logical Optimization
GetCurrentDatabase is a base logical optimization that gives the current database for current_database SQL function.
GetCurrentDatabase is part of the Finish Analysis once-executed batch in the standard batches of the Catalyst Optimizer.
GetCurrentDatabase is simply a Catalyst rule for transforming logical plans, i.e. Rule[LogicalPlan].
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val q = sql("SELECT current_database() AS db") val analyzedPlan = q.queryExecution.analyzed scala> println(analyzedPlan.numberedTreeString) 00 Project [current_database() AS db#22] 01 +- OneRowRelation import org.apache.spark.sql.catalyst.optimizer.GetCurrentDatabase val afterGetCurrentDatabase = GetCurrentDatabase(spark.sessionState.catalog)(analyzedPlan) scala> println(afterGetCurrentDatabase.numberedTreeString) 00 Project [default AS db#22] 01 +- OneRowRelation |
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Note
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You can access the current database in Scala using
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Executing Rule — apply Method
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apply(plan: LogicalPlan): LogicalPlan |
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Note
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apply is part of the Rule Contract to execute (apply) a rule on a TreeNode (e.g. LogicalPlan).
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apply…FIXME
