diff --git a/Notes b/Notes
index c550b96..fe05999 100644
--- a/Notes
+++ b/Notes
@@ -127,3 +127,12 @@ are hardlinked to older instances. Example (on mri):
 | 3225686 | f         |     65559 | 1260229629 | hjp        | betreuer   | u::rw-,g::r--,o:r-- |                |      NULL | NULL                                     | NULL            |
 +---------+-----------+-----------+------------+------------+------------+---------------------+----------------+-----------+------------------------------------------+-----------------+
 
+Find files with checksum is null:
+
+select versions2.id, prefix, path  from versions2, instances, files, sessions 
+where file_type = 'f' and checksum is null
+  and versions2.id=instances.version
+  and instances.file=files.id
+  and instances.session=sessions.id
+limit 100000;
+