Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/18559#discussion_r126083002 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala --- @@ -751,15 +751,17 @@ class AstBuilder extends SqlBaseBaseVisitor[AnyRef] with Logging { * hooks. */ override def visitAliasedQuery(ctx: AliasedQueryContext): LogicalPlan = withOrigin(ctx) { - // The unaliased subqueries in the FROM clause are disallowed. Instead of rejecting it in - // parser rules, we handle it here in order to provide better error message. - if (ctx.strictIdentifier == null) { - throw new ParseException("The unaliased subqueries in the FROM clause are not supported.", - ctx) + val alias = if (ctx.strictIdentifier == null) { + // For un-aliased subqueries, use a default alias name that is not likely to conflict with + // normal subquery names, so that parent operators can only access the columns in subquery by + // unqualified names. Users can still use this special qualifier to access columns if they + // know it, but that's not recommended. + "_auto_generated_subquery_name" --- End diff -- How about using two underscores? `__spark_auto_generated_subquery_name`?
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