title: select values matching value from other column in the same table
body: <p>I need help writing a query. What I'm trying to do, is to check, if any category_id have both (or even more) given tag_id's. I'm looking for most optimal query...</p>
  
  <p>if any category_id have both (or even more) tag_id's</p>
  
  <pre><code>id              int(10) NO  PRI     auto_increment
  client_id       int(10) YES         
  category_id     int(10) YES         
  tag_id          int(10) YES 
  </code></pre>
  
  <p>sample data:</p>
  
  <pre><code>41  1   137 183
  40  1   137 124
  39  1   136 179
  38  1   136 124
  62  1   143 263
  61  1   143 200
  60  1   143 135
  59  1   143 131
  58  1   143 125
  </code></pre>