title: update and concatenate columns in PostgreSQL
body: <p>I want to update and concatenate 3 columns in a new a attribute I've already created in my table. However when I execute my code, it puts attributes that before had values in <code>null</code>.</p>
  
  <p>My code example:  </p>
  
  <pre><code>update saber2012_1
      set estu_fecha_nacimiento = Concat(estu_nacimiento_dia,'/',estu_nacimiento_mes,'/',estu_nacimiento_anno); 
  </code></pre>
  
  <p>In this picture all values that is in <code>null</code> before these had values.</p>
  
  <p><img src="https://i.stack.imgur.com/9PfPK.png" alt="enter image description here"></p>
  
  <p>when I make this update   </p>
  
  <pre><code>ALTER TABLE saber2012_uno ADD COLUMN punt_c_naturales int;
  update saber2012_uno set punt_c_naturales = round((PUNT_BIOLOGIA::numeric + PUNT_FISICA::numeric + PUNT_QUIMICA::numeric) / 3,0); 
  alter table saber2012_uno DROP COLUMN PUNT_BIOLOGIA; 
  alter table saber2012_uno DROP COLUMN PUNT_FISICA;
  alter table saber2012_uno DROP COLUMN PUNT_QUIMICA;     
  </code></pre>
  
  <p>all is well. but I do not know because previous update is incorrect.                                                  </p>