silundong commented on code in PR #4400:
URL: https://github.com/apache/calcite/pull/4400#discussion_r2107006293
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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:
I think the simplification of idempotency alone is not sufficient. It should
be combined with general simplification. For example, if the third operand is
not trim but another `RexCall`, there is a lack of simplification for it.
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