I haven't tried it, but SQLFairy looks useful. It's a set of Perl modules that

manipulate structure data definitions (mostly database schemas) in interesting ways, such as converting among different dialects of CREATE syntax (e.g., MySQL-to-Oracle), visualizations of schemas (pseudo-ER diagrams GraphViz or GD), automatic code generation (using Class::DBI), converting non-RDBMS files to SQL schemas (xSV text files, Excel spreadsheets), serializing parsed schemas (via Storable, YAML and XML), creating documentation (HTML and POD), and more.