[SPARK-22553] Drop FROM in nonReserved

• Type: Improvement
• Status: Resolved
• Priority: Trivial
• Resolution: Incomplete
• Affects Version/s: 2.2.0
• Component/s: SQL
• Labels: bulk-closed
• Assignee: Unassigned
• Reporter: Takeshi Yamamuro
• Created: 19/Nov/17 01:31
• Updated: 31/May/19 17:44
• Resolved: 21/May/19 04:15

Description

A simple query below throws a misleading error because nonReserved has `SELECT` in SqlBase.q4:

scala> Seq((1, 2)).toDF("a", "b").createTempView("t")
scala> sql("select a, count(1), from t group by 1").show
org.apache.spark.sql.AnalysisException: cannot resolve '`a`' given input columns: []; line 1 pos 7;
'Aggregate [unresolvedordinal(1)], ['a, count(1) AS count(1)#13L, 'from AS t#11]
+- OneRowRelation$

  at org.apache.spark.sql.catalyst.analysis.package$AnalysisErrorAt.failAnalysis(package.scala:42)
  at org.apache.spark.sql.catalyst.analysis.CheckAnalysis$$anonfun$checkAnalysis$1$$anonfun$apply$2.applyOrElse(CheckAnalysis.scala:88)
  at org.apache.spark.sql.catalyst.analysis.CheckAnalysis$$anonfun$checkAnalysis$1$$anonfun$apply$2.applyOrElse(CheckAnalysis.scala:85)
  at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$transformUp$1.apply(TreeNode.scala:289)

I know nonReserved currently has `SELECT` because of the historical reason (https://github.com/apache/spark/pull/18079#discussion_r118842186). But, since IMHO this is a kind of common mistakes (This message annoyed me a few days ago in large SQL queries...), it might be worth dropping it in the reserved.

FYI: In postgresql throws an explicit error in this case:

postgres=# select a, count(1), from test group by b;
ERROR:  syntax error at or near "from" at character 21
STATEMENT:  select a, count(1), from test group by b;
ERROR:  syntax error at or near "from"
LINE 1: select a, count(1), from test group by b;

Issue Links

• Is contained by: SPARK-26215 define reserved keywords after SQL standard