How to determine if a variable has a special character using double table on sql?


I'm currently trying to check if a string has a special character (value that is not 0 to 9 A to Z a to z), but the inhouse language that I'm currently using has a very limited function to do it (possible but it will take a lot of lines). but I am able to do a query on sql. Now I would like to ask if it is possible to query using the dual table on sql, My plan is to pass the string to variable and this variable will be use on my sql command. Thanks in advance.

Here is what you can use

SELECT REGEXP_INSTR('Test!ing','[^[:alnum:]]') FROM dual;

This will return a number other than 0 whenever your string has anything other than letters or numbers.