# HG changeset patch
# User Sascha Wilde <wilde@intevation.de>
# Date 1568990300 -7200
# Node ID a3cbf5a2c1ef1845d7888b13b49b57213fed90d7
# Parent  5e62c467e145073114cb1f42aeeebced4621037b
Clarify that db update scripts must not include regular schema files.

diff -r 5e62c467e145 -r a3cbf5a2c1ef schema/updates/README.md
--- a/schema/updates/README.md	Fri Sep 20 13:52:19 2019 +0200
+++ b/schema/updates/README.md	Fri Sep 20 16:38:20 2019 +0200
@@ -22,6 +22,10 @@
 SELECT get_schema_version();
 ```
 
+It is an design goal to allow any older version of a gemma data base
+to be updated to the most current schema by calling `update-db.sh`
+from the current gemma distribution.
+
 ## Directory Layout
 
 the `schema/updates` directory contains subdirectories with names
@@ -63,6 +67,13 @@
   Note that all scripts in one version update are executed in a single
   transaction by the `update-db.sh` script.
 
+  **Important:** all sql scripts in one update directory have to be
+  self contained and *must not* include any files from the regular
+  schema definition (or from other update versions).  This is
+  necessary to allow for updates over multiple versions of the schema,
+  where multiple updates might make incremental changes to the same
+  functions/files of the schema.
+
 - Modify the scripts in `schema/` (outside the updates directory) to
   reflect the changes.  The schema of a freshly created database using
   `schema/install-db.sh` must always be identical to the schema of a