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

["cloud-fan (via GitHub)" <gi...@apache.org>]

cloud-fan commented on code in PR #40126:
URL: https://github.com/apache/spark/pull/40126#discussion_r1129378877


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala:
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@@ -465,7 +465,23 @@ class Analyzer(override val catalogManager: CatalogManager) extends RuleExecutor
   }
 
   /**
-   * Replaces [[UnresolvedAlias]]s with concrete aliases.
+   * Replaces [[UnresolvedAlias]]s with concrete aliases by applying the following rules:
+   *   1. Use the specified name of named expressions;
+   *   2. Derive stable aliases from the lexer tree of the original SQL text by concatenating of
+   *      terms via a single space, and applying the additional rules:
+   *     2.0. Don't add a space between terms if at least one of them contains a char which is not
+   *          a letter and a digit.
+   *     2.1. Normalize SQL string literals when ANSI mode is enabled and the SQL config
+   *          `spark.sql.ansi.doubleQuotedIdentifiers` is set to `true`.
+   *          For example: "abc" => 'abc'
+   *     2.2. A multipart identifier (column, field, mapkey, ...) -> the right most identifier.
+   *          For example: a.b.c => c
+   *     2.3. A CAST, or try_cast -> the argument of the cast.
+   *          For example: CAST(c1 AS INT) => c1
+   *     2.4. A map lookup with a literal -> the map key.
+   *          For example: map[5] => 5

Review Comment:
   is this really what we want? what was the previous behavior?



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