Forget SQL and get down to some basic statistics. You can never be sure whether someone is or isn't filling in your form in good faith, even if they put down five 0s in a row (or some other such 'indicator'). If you get enough respondents all the outliers will fade into background noise.
In fact there are statistical analyses of random responding, which I am referring to for this purpose. I would still like to know how to detect strings of the same number - the interpretation is a seperate issue.