RegexReplace() is a scalar function that lets you find-and-replace inside a string using regular expressions. RegexReplace() is a SQL CLR function that exposes the System.Text.RegularExpressions' Replace() method.
Let's look at a few examples, inspired by another handy Regular Expressions tutorial
Change a sentence
select dbo.RegexReplace('Hello, my name is John Doe', 'my name is (.+)', 'my name is not $1')