SQL Alias is something which you may have to create when you’re moving your database server. I had a requirement to move from an old database server to new one and as a part of the migration had to create SQL Alias. This is how you create it.
You will have to create SQL Alias on each web front and application server of SharePoint.
Click on Start > Run and Type cliconfg
Click on Ok
Now enable TCP/IP Protocol.
Select TCP/IP and Click on Enable
Click on Alias Tab
Click on Add
Select TCP/IP from Network Libraries
And enter the old database server name in Server Alias
And set the Server Name to New Database Server Name