Do we need to install SQL Express edition prior installing SharePoint 2010 server? Or the Standalone approach by default installs SQL Express DB ?
If you select standalone installation option then it will automatically install the Sql server express edition along with it.
I did not try to install SP2010 standalone but SP2013 installs SQL Server 2008 R2 Express by default when you install SP2013 only. I guess SP2010 does same.
Also found this link
Yes, you need to install SQL Express.
You can refer to the following article:
This is a reference about how to install the SQL server express: