title: Postgresql Concat String
body: <p>I want to create select Query in Postgresql. my code is</p>
  
  <pre><code> select * into concat('production.',layer_name)  from concat('staging.',layer_name); 
  </code></pre>
  
  <p>but there is a problem</p>
  
  <pre><code>ERROR:  "concat" is not a known variable
  LINE 20: select * into concat('production.'layer_name)  from concat('...
  </code></pre>
  
  <p>I can not understand why .</p>
  
  <p>Can anybody help me?</p>