Merge branch '5629' into 'stable-3.1'

update sql patch instructions.

See merge request ispconfig/ispconfig3!1006

Author: Till Brehm

install/sql/README.txt

@@ -9,15 +9,24 @@ then follow these steps:
 1) Add the field or table in the ispconfig3.sql file. This file contains the
    complete database dump which is used when ISPConfig gets installed.
 
-2) Add your ALTER TABLE, or if it is a complete new table then the add table,
-   statement(s) in MySQL syntax which is/are required to modify the current
-   ispconfig database during update to the file upd_dev_collection.sql in the
-   sql/incremental subfolder.
+2) Edit the file "incremental/upd_dev_collection.sql" which contains the SQL
+   statements (alter table, add table, update, etc.) in MySQL syntax which
+   are required to modify the current ispconfig database during update.
+
+   The upd_dev_collection.sql file contains all db schema modifications
+   for changes made since the last ISPConfig release.  If SQL statements
+   are already present in the file when you make your additions, add yours
+   to the end of the file, and do not remove any existing statements.
+
+   When a new ISPConfig update is released, the contents of
+   upd_dev_collections.sql will move to an sql patch file, using the naming
+   scheme upd_0001.sql, upd_0002.sql, upd_0003.sql etc.
 
-   Please do not create new patch sql files as those will be generated on
-   new releases from the upd_dev_collection.sql file. Also please do not
-   modify older (already released) patch files, they will not get executed
-   again if the update was already run once on a system.
+   A patch file may contain one or more SQL modification statements. Every patch
+   file gets executed once in the database, so do not modify older (already released)
+   patch files, they will not get executed again if the update was already run 
+   once on a system, and will result in missing updates on any system where they
+   have not run yet.
 
    After a patch has been executed, the dbversion field in the server table gets
    increeased to the version number of the last installed patch.