title: What does double bars (||) mean in SQL?
body: <p>I'm trying to understand the following query:
  <br/><code>select count(distinct Name || '' || Surname) from PEOPLE;</code>
  <br/>What does the double bars mean? What does this query do?</p>
  
  <p><br/>In MySQL:<br/>
  <code>select  "aaaaa" || '' || "bbbbb";</code></p>
  
  <p><code>+--------------------------+
  | "aaaaa" || '' || "bbbbb" |
  +--------------------------+
  |                        0 |
  +--------------------------+
  </code></p>