One tool I just discovered from www.orm.net is Microsoft's free (unsupported) download of VisioModeler. This is now integrated with Visio Enterprise Architect, but the original software is kept around for some reason.
While this is a complex, very advanced tool for Object Role Modeling, it also allows you to create other types of logical models, including ER diagrams. If you play around with it enough, you will see that it can generate diagrams by connecting to ODBC sources, and it can generate databases and/or SQL scripts based on your diagram changes.
Originally posted by Tylon
Anyone know any software that would allow me to generate ER diagrams from an existing Access or MySQL database? I am looking for a free method - trial versions are fine.
DB Designer 4 is open source, runs on Windows, and does MySQL. If you're using InnoDB tables and foreign keys, it doesn't derive the FK relationships from the table definitions (it uses column names to 'estimate' them, which cannot do the whole job when you refer to a table multiple times from the same table). Other than that, it's very good. It's newly released, too, and is being developed very quickly, so now is the time to get involved in this one and suggest your favourite features.
Access will generate it's own ER diagrams - just use the 'relationships' tool. Microsoft provides an add-in for Access 97 to print the relationships window out. (I think it might be included in subsequent versions - not sure.)