1 files changed, 18 insertions, 8 deletions
diff --git a/sqlglot/expressions.py b/sqlglot/expressions.py
index f8e9fee..c207751 100644
--- a/sqlglot/expressions.py
+++ b/sqlglot/expressions.py
@@ -192,6 +192,13 @@ class Expression(metaclass=_Expression):
         return self.text("alias")
 
     @property
+    def alias_column_names(self) -> t.List[str]:
+        table_alias = self.args.get("alias")
+        if not table_alias:
+            return []
+        return [c.name for c in table_alias.args.get("columns") or []]
+
+    @property
     def name(self) -> str:
         return self.text("this")
 
@@ -884,13 +891,6 @@ class Predicate(Condition):
 
 class DerivedTable(Expression):
     @property
-    def alias_column_names(self) -> t.List[str]:
-        table_alias = self.args.get("alias")
-        if not table_alias:
-            return []
-        return [c.name for c in table_alias.args.get("columns") or []]
-
-    @property
     def selects(self) -> t.List[Expression]:
         return self.this.selects if isinstance(self.this, Subqueryable) else []
 
@@ -4860,8 +4860,18 @@ def maybe_parse(
     return sqlglot.parse_one(sql, read=dialect, into=into, **opts)
 
 
+@t.overload
+def maybe_copy(instance: None, copy: bool = True) -> None:
+    ...
+
+
+@t.overload
 def maybe_copy(instance: E, copy: bool = True) -> E:
-    return instance.copy() if copy else instance
+    ...
+
+
+def maybe_copy(instance, copy=True):
+    return instance.copy() if copy and instance else instance
 
 
 def _is_wrong_expression(expression, into):