[GitHub] [druid] ccaominh commented on a change in pull request #9384: Add join prefix duplicate/shadowing check

[GitBox <gi...@apache.org>]

ccaominh commented on a change in pull request #9384: Add join prefix duplicate/shadowing check
URL: https://github.com/apache/druid/pull/9384#discussion_r384184065
 
 

 ##########
 File path: processing/src/main/java/org/apache/druid/segment/join/Joinables.java
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 @@ -114,4 +122,45 @@ public static boolean isPrefixedBy(final String columnName, final String prefix)
       );
     }).collect(Collectors.toList());
   }
+
+  private static void checkPreJoinableClausesForDuplicatesAndShadowing(
+      final List<PreJoinableClause> preJoinableClauses
+  )
+  {
+    List<String> prefixes = new ArrayList<>();
+    for (PreJoinableClause clause : preJoinableClauses) {
+      prefixes.add(clause.getPrefix());
+    }
+
+    checkPrefixesForDuplicatesAndShadowing(prefixes);
+  }
+
+  /**
+   * Check if any prefixes in the provided list duplicate or shadow each other.
+   *
+   * @param prefixes A mutable list containing the prefixes to check. This list will be sorted by descending
+   *                 string length.
+   */
+  public static void checkPrefixesForDuplicatesAndShadowing(
+      final List<String> prefixes
+  )
+  {
+    // this is a naive approach that assumes we'll typically handle only a small number of prefixes
+    prefixes.sort(DESCENDING_LENGTH_STRING_COMPARATOR);
+    for (int i = 0; i < prefixes.size(); i++) {
+      String prefix = prefixes.get(i);
+      for (int k = i; k < prefixes.size(); k++) {
+        if (i != k) {
 
 Review comment:
   Can the check for `i != k` be removed if `k` is initialized to `i + 1`?

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