title: How to escape parentheses in a REGEXP clause
body: <p>In my database I have some keys like this:</p>
  
  <pre><code>custom_field_languages(0)language
  custom_field_languages(1)language
  custom_field_languages(2)language
  ...
  </code></pre>
  
  <p>And I need all of them. But this doesn't work:</p>
  
  <pre><code>REGEXP '^custom_field_languages([0-9])language'
  </code></pre>
  
  <p>This also doesn't work.</p>
  
  <pre><code>REGEXP '^custom_field_languages\([0-9]\)language'
  </code></pre>
  
  <p>This works but isn't 100% accurate.</p>
  
  <pre><code>REGEXP '^custom_field_languages.[0-9].language'
  </code></pre>
  
  <p>What is the correct way to escape normal parentheses?</p>