I have website called xyz.com, and added additional store called abc.xyz.com, now i have purchased new domain 123.com. How can i redirect my subdomain as new domain, like if customer enter 123.com it will be redirect to abc.xyz.com, and url should be like 123.com not changing to abc.xyz.com in the url bar.
Well you can do it this from DNS settings of your domain name server , you actually don't need to do anything at magento side.
Most of all the domain panel have this settings to redirect domain to another domain - so you can achieve from there only !
But as you mention that you also don't wanted to change the URL - so i think that 's near to impossible as you are redirecting domain - then off course after redirecting URL should be a that new domain only !
or else if you still wanted to achieve that then you need to load your full application on the new domain as well
Hope it helps