Klaasvaak

Instead of using regexp like so:
ancestors column would be something like: {"category": 1}
WHERE  `ancestors` REGEXP '(.*\"category\":\"1\")'

Use the JSON functions:
WHERE JSON_EXTRACT(`ancestors`, 'category') = 1

Arrays:
WHERE JSON_SEARCH(JSON_EXTRACT('{"categories": [1,2,3]}', 'categories'), "1") != null

Klaasvaak

const cities = ['rome', 'madrid', 'paris', 'brussels', 'eindhoven', 'berlin', 'copenhagen', 'stockholm'];
const myAwesomeSearch = value => cities.filter(city => city.indexOf(value) !== -1);

const input = document.querySelector('input');
const suggestions = document.querySelector('#suggestions');

Rx.Observable.fromEvent(input, 'keyup')
  .pluck('target', 'value')
  .map(value => myAwesomeSearch(value))
  .map(cities => cities.map(city => `<li>${city}</li>`).join(''))