title: How to restrict values in MySQL insert?
body: <p>So I have a simple database exercise at school and I'm nearly finished but I don't know how to restrict values.</p>
  
  <p>I have a database like:</p>
  
  <pre>
  ID | Name | Age
   1 | John | 20
   2 | Jack | 30
  </pre>
  
  <p>And so on.</p>
  
  <p>Is there a way to prevent users from inserting an age lower than 18?
  I've been searching a lot and didn't find the answer... Thanks in advance!</p>