xuzifu666 commented on code in PR #4400:
URL: https://github.com/apache/calcite/pull/4400#discussion_r2106960592


##########
core/src/main/java/org/apache/calcite/rex/RexSimplify.java:
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@@ -2364,6 +2366,37 @@ private RexNode simplifyCeilFloor(RexCall e) {
         ImmutableList.of(operand, e.getOperands().get(1)));
   }
 
+  /** Simplify TRIM function by eliminating nested duplication.
+   *
+   * <p>Examples:
+   * <ul>
+   *
+   * <li>{@code trim(trim(' aa '))} returns {@code trim(' aa ')}
+   *
+   * <li>{@code trim(BOTH ' ' from trim(BOTH ' ' from ' aa '))}
+   * returns {@code trim(BOTH ' ' from ' aa ')}
+   *
+   * <li>{@code trim(LEADING 'a' from trim(BOTH ' ' from ' aa '))} does not 
change
+   *
+   * </ul>
+   */
+  private RexNode simplifyTrim(RexCall e) {
+    if (e.getOperands().size() != 3) {
+      return e;
+    }
+
+    if (e.getOperands().get(2) instanceof RexCall) {

Review Comment:
   Yes, trim function would convert as trim(both/leading/tailing ' ' from 
expression). 
   Only expresstion need to be handle because it maybe a string or a expression 
like trim(...) @silundong 



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