[GitHub] [spark] melihsozdinler commented on a diff in pull request #40474: [SPARK-42849] [SQL] Session Variables

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

melihsozdinler commented on code in PR #40474:
URL: https://github.com/apache/spark/pull/40474#discussion_r1285899298


##########
sql/core/src/main/scala/org/apache/spark/sql/execution/SparkSqlParser.scala:
##########
@@ -567,6 +568,135 @@ class SparkSqlAstBuilder extends AstBuilder {
     }
   }
 
+  /**
+   * Create a [[CreateVariableCommand]].
+   *
+   * For example:
+   * {{{
+   *   DECLARE [OR REPLACE] [VARIABLE] [db_name.]variable_name
+   *   [dataType] [defaultExpression];
+   * }}}
+   *
+   * We will ad CREATE VARIABLE for persisted variable definitions to this, hence the name...
+   */
+  override def visitCreateVariable(ctx: CreateVariableContext): LogicalPlan = withOrigin(ctx) {
+
+    def format(name: String): String = {
+      if (conf.caseSensitiveAnalysis) name else name.toLowerCase(Locale.ROOT)
+    }
+
+    val multipartIdentifier = visitMultipartIdentifier(ctx.multipartIdentifier)
+    val defaultExpression = if (ctx.variableDefaultExpression() == null) {
+      "null"
+    } else {
+      visitVariableDefaultExpression(ctx.variableDefaultExpression())
+    }
+    val dataTypeStr: Option[String] =
+      if (Option(ctx.dataType).nonEmpty) {
+        Option(source(Option(ctx.dataType).get))
+      } else {
+        Option(null)
+      }
+
+    if (multipartIdentifier.length > 3) {
+      throw QueryParsingErrors.unsupportedVariableNameError(
+        multipartIdentifier, ctx.multipartIdentifier)
+    }
+
+    val schemaQualifiedName = if (multipartIdentifier.length < 2) {
+      SESSION_DATABASE +: multipartIdentifier
+    } else {
+      multipartIdentifier
+    }
+
+    val catalogQualifiedName = if (schemaQualifiedName.length < 3) {

Review Comment:
   This "3" and VariableIdentifier apply method checks length 3 are connected? If connected there should be some comment to change also inside the apply function, or we can avoid such magic number issues by targetting named some meaningful variable with a value 



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