Andrew Ash created SPARK-22204:
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Summary: Explain output for SQL with commands shows no optimization
Key: SPARK-22204
URL: https://issues.apache.org/jira/browse/SPARK-22204
Project: Spark
Issue Type: Bug
Components: SQL
Affects Versions: 2.3.0
Reporter: Andrew Ash
When displaying the explain output for a basic SELECT query, the query plan
changes as expected from analyzed -> optimized stages. But when putting that
same query into a command, for example {{CREATE TABLE}} it appears that the
optimization doesn't take place.
In Spark shell:
Explain output for a {{SELECT}} statement shows optimization:
{noformat}
scala> spark.sql("SELECT a FROM (SELECT a FROM (SELECT a FROM (SELECT 1 AS a)
AS b) AS c) AS d").explain(true)
== Parsed Logical Plan ==
'Project ['a]
+- 'SubqueryAlias d
+- 'Project ['a]
+- 'SubqueryAlias c
+- 'Project ['a]
+- SubqueryAlias b
+- Project [1 AS a#29]
+- OneRowRelation
== Analyzed Logical Plan ==
a: int
Project [a#29]
+- SubqueryAlias d
+- Project [a#29]
+- SubqueryAlias c
+- Project [a#29]
+- SubqueryAlias b
+- Project [1 AS a#29]
+- OneRowRelation
== Optimized Logical Plan ==
Project [1 AS a#29]
+- OneRowRelation
== Physical Plan ==
*Project [1 AS a#29]
+- Scan OneRowRelation[]
scala>
{noformat}
But the same command run inside {{CREATE TABLE}} does not:
{noformat}
scala> spark.sql("CREATE TABLE IF NOT EXISTS tmptable AS SELECT a FROM (SELECT
a FROM (SELECT a FROM (SELECT 1 AS a) AS b) AS c) AS d").explain(true)
== Parsed Logical Plan ==
'CreateTable `tmptable`, org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe,
Ignore
+- 'Project ['a]
+- 'SubqueryAlias d
+- 'Project ['a]
+- 'SubqueryAlias c
+- 'Project ['a]
+- SubqueryAlias b
+- Project [1 AS a#33]
+- OneRowRelation
== Analyzed Logical Plan ==
CreateHiveTableAsSelectCommand [Database:default}, TableName: tmptable,
InsertIntoHiveTable]
+- Project [a#33]
+- SubqueryAlias d
+- Project [a#33]
+- SubqueryAlias c
+- Project [a#33]
+- SubqueryAlias b
+- Project [1 AS a#33]
+- OneRowRelation
== Optimized Logical Plan ==
CreateHiveTableAsSelectCommand [Database:default}, TableName: tmptable,
InsertIntoHiveTable]
+- Project [a#33]
+- SubqueryAlias d
+- Project [a#33]
+- SubqueryAlias c
+- Project [a#33]
+- SubqueryAlias b
+- Project [1 AS a#33]
+- OneRowRelation
== Physical Plan ==
CreateHiveTableAsSelectCommand CreateHiveTableAsSelectCommand
[Database:default}, TableName: tmptable, InsertIntoHiveTable]
+- Project [a#33]
+- SubqueryAlias d
+- Project [a#33]
+- SubqueryAlias c
+- Project [a#33]
+- SubqueryAlias b
+- Project [1 AS a#33]
+- OneRowRelation
scala>
{noformat}
Note that there is no change between the analyzed and optimized plans when run
in a command.
This is misleading my users, as they think that there is no optimization
happening in the query!
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