title: How to delete rows which can't be cast to INT
body: <p>I have this sample table with a housenumber in my postgresql 9.1:</p>
  
  <pre><code>drop table if exists mytable;
  create table mytable(road_id int, housenr text);
  insert into mytable(road_id, housenr) values
  
  ('11', '1' ),
  ('22', '12' ), 
  ('33', '99/1' ),
  ('44', '88' ),
  ('55', '2' ),
  ('66', '28' ),
  ('77', '29')
  ;
  </code></pre>
  
  <p>Now I have to convert the whole column "housenr" into an INT field. Is there a way in SQL to cast only these rows from the column which can be casted. In mytable this would be every row except the one with "housenr" = 99/1.<br>
  Something like: FOR EACH ROW IF ::int IS POSSIBLE cast the row ELSE REMOVE FROM TABLE</p>