TSQL: Special (National) char detection (SQL Server2016) - tsql

Question

I found a lot of techniques to detect aka special chars($%##) avail on English keyboard, however I see that some national char like á works differently, though my LIKE condition should get it, as it should select anything but a-z1-9, what is the trick here: In sample below I'm missing my special á. I'm on TSQL 2016 with default settings in US.
;WITH cte AS (SELECT 'Euro a€' St UNION SELECT 'adgkjb$' St UNION SELECT 'Bravo Endá' St)
SELECT * FROM cte WHERE St LIKE '%[^a-zA-Z0-9 ]%'
St
adgkjb$
Euro a€
SELECT CAST(N'€' AS VARBINARY(8)) --0xAC20
SELECT CAST(N'á' AS VARBINARY(8)) --0xE100

Answer 1

SQL Server appears to be helping with ranges of characters due to the default collation. If you explicitly list all of the valid characters it will work as desired. Alternatively, you can force a collation on the pattern match that won't interpret the pattern a containing non-ASCII characters.
-- Explicit pattern for "bad" characters.
declare #InvalidCharactersPattern as VarChar(100) = '%[^abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 ]%';
-- Query some sample data with the explicit pattern and an explicitly specified collation.
select Sample,
case when Sample like #InvalidCharactersPattern then 'Bad Character' else 'Okay' end as ExplicitStatus,
case when Sample like '%[^a-zA-Z0-9 ]%' collate Latin1_General_100_BIN
then 'Bad Character' else 'Okay' end as CollationStatus
from ( values ( 'a' ), ( 'A' ), ( 'á' ), ( 'Foo' ), ( 'F&o' ), ( '$%^&' ) ) as Samples( Sample );
-- Server collation.
select ServerProperty( 'collation' ) as ServerCollation;
-- Available collations.
select name, description
from sys.fn_helpcollations()
order by name;