Question mark is not visible

Question

select case when 'A​B' = 'A?B' then 1 else 0 end

Result:1

Why is the question mark in the first string not visible？

Does anyone know a fix for this?

Answer 1

That first 'AB' is really (A) (zero width space) (B).

For SqlServer a quoted string without an N prefix is treated as a single-byte-per-character string. Apparently the "non ascii" zero width space is translated into a question mark before comparing.

Adding the "N-prefix" gives the expected result (0):

select case when N'A​B' = N'AB' then 1 else 0 end