SELECT FROM <table_name>
WHERE REGEXP_LIKE(<column_name>, '[[:<POSIX_CHAR_CODE:]]');
 
-- example to search for a TAB character (ASCII 9):
SELECT *
FROM sandbox
WHERE REGEXP_LIKE(regex_test, '[[:TAB:]]{1}');
 
 
-- example to search for any 2 digits
SELECT *
FROM sandbox
WHERE REGEXP_LIKE(regex_test, '[[:digit:]]{2}');
 
 
-- example to search for lowercase characters
SELECT *
FROM sandbox
WHERE REGEXP_LIKE(regex_test, '[[:lower:]]');
 
 
-- or, search for UPPERCASE characters. In this 
-- case we're looking for four (4) characters 
SELECT *
FROM sandbox
WHERE REGEXP_LIKE(regex_test, '[[:upper:]]{4}');
 
 
-- example to search for printable characters
-- this example looks for three printable characters 
-- as specified by the '{3}' quantifier 
SELECT *
FROM sandbox
WHERE REGEXP_LIKE(regex_test, '[[:print:]]{3}');
 
 
-- example to search for whitespace characters. 
-- this includes space, tab, NL, FF, VT, and CR. 
SELECT *
FROM sandbox
WHERE REGEXP_LIKE(regex_test, '[[:space:]]');
 
-- search for a 'Q' in the fourth position. 
-- notice the start-of-line anchor, '^' is used. 
SELECT * 
FROM sandbox
WHERE REGEXP_LIKE(regex_text, '^...Q.');