Using "as" in DUAL statement produces error

Question

Hi,
SELECT 'abcefghijklm' AS str FROM DUAL WHERE str IN ('a','e','i','o','u');
This produces an error message - "STR": invalid identifier
Is such a comparison using a field name invented using "as" always invalid - is there no way around it?
What I am trying to do is to count the number of vowels in a sentence, there may be a better approach of course, if anyone knows one...?

Answer 1

What I am trying to do is to count the number of vowels in a sentence
SQL> select word_char,count(*) from (SELECT substr(str,ROWNUM,1) AS word_char
  2  FROM (SELECT 'abcefghijklmabcefghijklmno' as str FROM DUAL) CONNECT BY LEVEL <= length(str))
  3  where word_char IN ('a','e','i','o','u') group by word_char order by word_char;
W   COUNT(*)
a          2
e          2
i          2
o          1
SQL>
SQL> select length(str) - length(replace(translate(lower(str),'aeiou',' '),' ','')) cnt
  2  from (SELECT 'abcefghijklmabcefghijklm' as str FROM DUAL);
       CNT
         6
SQL>
SQL>