“ Database attach upgrades seem to be the norm these days for customers upgrade from SharePoint 2007 to SharePoint 2010. I am assuming the reason for this is because they are very flexible and generally work pretty well. One of the flexible things about these type of upgrades is you can change your web application URL. Some customers are going from short URL to fully qualified (FQDN) like http://portal tohttp://portal.company.com. And some of our customers are making complete changes going from http://sharepoint.company.com tohttp://intranet.company.com. The nice thing about making these types of changes is for the most part a content database has no concept of the web application URL. If you go hunting through the database (which you should never do) you will see everything is relative. The site collections know their urls as / or /sites/sitecollection. That way changing the URL doesn't matter.
But then there are alerts. Alerts are hard coded to the web application URL that was used to create the alert. This is why if you have multiple URLs for you SharePoint site your alerts may be inconsistent. If your portal is setup so you can access it as http://portal orhttp://portal.contoso.com then whichever of those URLs you are browsing the site with when you click create alert will be the URL SharePoint sends out in the alerts. Kind of annoying for some people but it is what it is. The real problem comes if you switch URLs.
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