fix(cubesql): Fix incorrect underscore truncation for aliases

Author: KSDaemon

rust/cubesql/cubesql/src/compile/engine/df/wrapper.rs

@@ -415,8 +415,14 @@ impl Remapper {
         static NON_ID_REGEX: LazyLock<Regex> =
             LazyLock::new(|| Regex::new(r"[^a-zA-Z0-9_]").unwrap());
 
-        let alias = start_from;
-        let mut truncated_alias = NON_ID_REGEX.replace_all(&alias, "_").to_lowercase();
+        let alias_lower = start_from.clone().to_lowercase();
+        let mut truncated_alias =
+            if !alias_lower.contains("__user") && !alias_lower.contains("__cubejoinfield") {
+                NON_ID_REGEX.replace_all(&alias_lower, "_").to_string()
+            } else {
+                alias_lower
+            };
+
         truncated_alias.truncate(16);
         let mut alias = truncated_alias.clone();
         for i in 1..10000 {