使用REGEXP进行搜索，MySQL中没有重复字符

Question

I have a databse of english words and i want to use regexp to search in this database i used this query :

SELECT * FROM `english` WHERE CHAR_LENGTH(words)=4  AND  `words` REGEXP '^[oofd]+$'

it is working and its selecting the words like food,foo,of,do but it is also selecting the words like fooo with 3 o's but in my regexp there is just 2 o's what is the right regular expression to select words with no repeating characters
if there is two character for example oo it will select just words with two o or 1 or zero , not three or more

I looked in the internet i came with this:

^(?:([oofd])(?!.*\1))

but it gives me an error:

#1139 - Got error 'repetition-operator operand invalid' from regexp

Answer 1

Check for the presence of two vowels in sequence and the absence of three or more vowels in sequence:

SELECT *
FROM english
WHERE
    words REGEXP '^.*[aeiou]{2}.*$' AND
    words NOT REGEXP '^.*[aeiou]{3}.*$'

If you only want to look for certain repeated vowels, you should be able to adapt this answer fairly easily.