title: Query based on custom field
body: <p>I have made <strong>custom fields</strong> using <a href="https://wordpress.org/plugins/advanced-custom-fields/" rel="nofollow noreferrer">advanced custom field plugin</a>. It has a field name school which includes choices such as <em>arts,education,engineering</em>.
  Now my problem is how can i <strong>query</strong> only those post who field is arts  using <strong>wpdb</strong>. sincerely i don't know <strong>wpdb</strong> works.
  <img src="https://i.stack.imgur.com/H69Ax.png" alt="custom fields">.
  Any help will be appreciated :)</p>