[GitHub] [spark] MaxGekk commented on a diff in pull request #40126: [SPARK-40822][SQL] Stable derived column aliases

["MaxGekk (via GitHub)" <gi...@apache.org>]

MaxGekk commented on code in PR #40126:
URL: https://github.com/apache/spark/pull/40126#discussion_r1119846624


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala:
##########
@@ -669,17 +669,26 @@ class AstBuilder extends SqlBaseParserBaseVisitor[AnyRef] with SQLConfHelper wit
     )
   }
 
+  private def getAliasFunc(alias: => String): Option[Expression => String] = {
+    if (conf.getConf(SQLConf.STABLE_DERIVED_COLUMN_ALIAS_ENABLED)) {
+      Some(_ => alias)
+    } else {
+      None
+    }
+  }
+
   override def visitNamedExpressionSeq(
-      ctx: NamedExpressionSeqContext): Seq[Expression] = {
+      ctx: NamedExpressionSeqContext): Seq[(Expression, Option[Expression => String])] = {
     Option(ctx).toSeq
       .flatMap(_.namedExpression.asScala)
-      .map(typedVisit[Expression])
+      .map(ctx => (typedVisit[Expression](ctx), getAliasFunc(toExprAlias(ctx))))

Review Comment:
   Just in case, this function handle not only named expressions but others too. For example:
   ```sql
   select 1;
   ```
   is handled by `visitNamedExpressionSeq()` but not by `visitExpressionSeq()`.



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