Fix typo

Author: RobertRosca

docs/advanced/sa-column.md

@@ -2,7 +2,7 @@
 
 In some cases you may need more control over the columns generated by SQLModel, this can be done by using the `sa_column`, `sa_column_args`, and `sa_column_kwargs` arguments when creating the `Field` object.
 
-There are many use cases for this, but ones where this is particularity useful is when you want more advanced defaults for values than what is easy to implement with Pydantic, such `created_at` or `update_at` timestamps for rows.().
+There are many use cases for this, but ones where this is particularity useful is when you want more advanced defaults for values than what is easy to implement with Pydantic, such `created_at` or `update_at` timestamps for rows.
 
 ## Columns for Timestamps