How regular expression OR operator is evaluated

Question

In T-SQL I have generated UNIQUEIDENTIFIER using NEWID() function. For example:

723952A7-96C6-421F-961F-80E66A4F29D2

Then,

Answer 1

If you are interested in what happens when you use | alternation operator, the answer is easy: the regex engine processes the expression and the input string from left to right.

Taking the pattern you have as an example, ^.{8}|.{12}$|.{4} starts inspecting the input string from the left, and checks for ^.{8} - first 8 characters. Finds them and it is a match. Then, goes on and finds the last 12 characters with .{12}$, and again there is a match. Then, any 4-character strings are matched.

Debuggex Demo

Next, you have ^.{8}|.{4}|.{12}$. The expression is again parsed from left to right, first 8 characters are matched first, but next, only 4-character sequences will be matched, .{12} won't ever fire because there will be .{4} matches!

Debuggex Demo