I would like to migrate content db's, config DB and admin content DB from SQL server 2005 to SQL server 2008. Please let me know the procedure, how can I proceed with very minimal downtime.
To move SharePoint databases to different SQL server, the main steps as below:
Detatch the content, config and other related database from your SQL 2005 instance
Take copy of mdf and ldf files for these database
Move the mdf and ldf files to the SQL 2012
Attach the databases to SQL 2012
Re-run the SP 2010 configuration wizard
To get more detailed information, check the article: Moving SharePoint to a different SQL server