// Explain in SQL
scala> sql("EXPLAIN EXTENDED show tables").show(truncate = false)
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
|plan |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
|== Parsed Logical Plan ==
ShowTablesCommand
== Analyzed Logical Plan ==
tableName: string, isTemporary: boolean
ShowTablesCommand
== Optimized Logical Plan ==
ShowTablesCommand
== Physical Plan ==
ExecutedCommand
+- ShowTablesCommand|
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ExplainCommand Logical Command
ExplainCommand is a logical command that allows users to see how a structured query will be executed. It takes in a LogicalPlan and creates a QueryExecution that is used to output a single-column DataFrame with the following:
-
codegen explain, i.e. WholeStageCodegen subtrees if
codegenflag is enabled. -
extended explain, i.e. the parsed, analyzed, optimized logical plans with the physical plan if
extendedflag is enabled. -
simple explain, i.e. the physical plan only when no
codegenandextendedflags are enabled.
ExplainCommand is used for explain operator and EXPLAIN SQL statement (accepting EXTENDED and CODEGEN options).
The following EXPLAIN variants in SQL queries are not supported:
-
EXPLAIN FORMATTED -
EXPLAIN LOGICAL
scala> sql("EXPLAIN LOGICAL show tables")
org.apache.spark.sql.catalyst.parser.ParseException:
Operation not allowed: EXPLAIN LOGICAL(line 1, pos 0)
== SQL ==
EXPLAIN LOGICAL show tables
^^^
...