[SPARK-25769] UnresolvedAttribute.sql() incorrectly escapes nested columns - ASF JIRA

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Details

Type: Bug
Status: Resolved
Priority: Major
Resolution: Fixed
Affects Version/s: 2.3.2
Fix Version/s: 3.2.0
Component/s: SQL
Labels:
- pull-request-available

Description

UnresolvedAttribute.sql() output is incorrectly escaped for nested columns

import org.apache.spark.sql.catalyst.analysis.UnresolvedAttribute

// The correct output is a.b, without backticks, or `a`.`b`.
$"a.b".expr.asInstanceOf[UnresolvedAttribute].sql
// res1: String = `a.b`

// Parsing is correct; the bug is localized to sql() 
$"a.b".expr.asInstanceOf[UnresolvedAttribute].nameParts 
// res2: Seq[String] = ArrayBuffer(a, b)

The likely culprit is that the sql() implementation does not check for nameParts being non-empty.

override def sql: String = name match { 
  case ParserUtils.escapedIdentifier(_) | ParserUtils.qualifiedEscapedIdentifier(_, _) => name 
  case _ => quoteIdentifier(name) 
}