It is not uncommon for large companies to change their database platforms. There are many reasons for this, such as better security, more reliable technology, and better prices. However, the usual 13 weeks consumed at the re-platform operation may discourage most companies.
Maxis developed Alchemize, a heavy-duty software specialized in converting from one system to another, typically converting databases, for example, Oracle to SQL Server in hours.
Available at additional cost: