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

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

srielau commented on code in PR #40126:
URL: https://github.com/apache/spark/pull/40126#discussion_r1124536818


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala:
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@@ -465,7 +465,20 @@ 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 a stable alias from the original normalized SQL text except of:
+   *     2.1. A multipart identifier (column, field, mapkey, ...) -> the right most identifier.
+   *          For example: a.b.c => c
+   *     2.2. A CAST, or try_cast -> the argument of the cast.
+   *          For example: CAST(c1 AS INT) => c1
+   *     2.3. A map lookup with a literal -> the map key.
+   *          For example: map[5] => 5
+   *     2.4. Squeezing out unwanted whitespace or comments.
+   *          For example: T.c1 + /* test */ foo( 5 ) => T.c1+foo(5)
+   *     2.5. 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'

Review Comment:
   This description seems incomplete. I see examples below with \t, \r \n in strings. We preserve them? I'm doubtful that's useful).
   Also you seem to have some rules around whitespace.
   



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