I have released a version of the Moodle database entity relationship (ER) diagram generated from the
Moodle 2.9 code which can be found at
Although the tables in core Moodle do not change a much between releases this diagram is a little more ambitious than the previous ones. It incorporates relationships missing from the release code which can be found in this bug report
Also the SQL code that was used to reverse engineer the diagram included field comments. When Moodle is installed it will normally throw away all field level comments. I updated the code so it kept the comments. Due to some quirks the comments may be truncated but I decided some information is better than none.
This diagram is probably most helpful if you download the *.mwb file and load it up in MySQL workbench (a free cross platform tool) but I hope the graphics/png files are also useful. Check out the component diagrams as well at