Count occurrences of character in a string using MySQL

Question

Example Words: a, akkka, akokaa, kokoko, kakao, oooaooa, kkako, kakaoa

I need the regexp witch gives words with 2 or less \'a\' but not the words without \'a\'

Answer 1

I don't know what MySQL supports in terms of lookaround assertions, but the following will do the trick:

^(?=.*a.*a?.*)(?!.*a.*a.*a.*).*$

We have a lookahead assertion that matches 1 or 2 a characters in the string. Then we have a negative lookahead that disregards 3 or more as anywhere in the string. Then the final pattern just matches the whole string, providing the first two assertions are satisfied.

If MySQL doesn't support lookarounds, then @Woot4Moo's answer would be the way to go.