REGEXP_LIKE not returning expected results

Question

My first attempt at REGEXP_LIKE and I'm obviously missing something. I've tried several suggestions I found in the forum but cannot get the correct results. I need the following query to return only those rows containing only alphabetic characters (no numbers). What I get are rows containing letters and numbers.
Any help will be greatly appreciated!
Randy
SELECT order_number
FROM order_table
where REGEXP_LIKE(order_number,'[a-z A-Z]')

Answer 1

check below the various options which you can use to search different elements
Character Class   Syntax Meaning
[:alnum:]             All alphanumeric characters
[:alpha:]              All alphabetic characters
[:blank:]              All blank space characters
[:cntrl:]                All control characters (nonprinting)
[:digit:]                All numeric digits
[:graph:]             All [:punct:], [:upper:], [:lower:], and [:digit:] characters
[:lower:]              All lowercase alphabetic characters
[:print:]               All printable characters
[:punct:]              All punctuation characters
[:space:]             All space characters (nonprinting)
[:upper:]             All uppercase alphabetic characters
[:xdigit:]              All valid hexadecimal characters