title: ERROR: zero-length delimited identifier at or near """" LINE 1: DELETE FROM "regions" WHERE "regions"."" = $1
body: <p>I'm using Rails 4.1 and Postgresql (with PG gem) as my database. I have a very stand many to many association from companies to provinces with a join table called regions. Now obviously the regions table has no primary key cause I used { :id => false }. But when I try to use depending destroy or just simply calling destroy on the region object it self I get this error:</p>
  
  <pre><code> ERROR:  zero-length delimited identifier at or near """"
   LINE 1: DELETE FROM "regions" WHERE "regions"."" = $1
  </code></pre>
  
  <p>I know the problem is caused due to the lack of a primary key for the regions table. And oddly if I add the primary key back to the table destroy works fine and no error. However, if I remove the primary key from the table the error comes back. I know this has something to do with the postgres but I've no idea how to solve this without having to add a primary key column to my regions table.</p>
  
  <p>Here is the actual query</p>
  
  <pre><code>[DEBUG] [AdminUser Load (0.4ms)  SELECT  "admin_users".* FROM "admin_users"  WHERE "admin_users"."id" = 1  ORDER BY "admin_users"."id" ASC LIMIT 1] (pid:29655)
  [DEBUG] [Province Load (0.2ms)  SELECT  "provinces".* FROM "provinces"  WHERE "provinces"."id" = $1 LIMIT 1  [["id", 5]]] (pid:29655)
  [DEBUG] [ (0.1ms)  BEGIN] (pid:29655)
  [DEBUG] [Region Load (0.3ms)  SELECT "regions".* FROM "regions"  WHERE "regions"."province_id" = $1  [["province_id", 5]]] (pid:29655)
  [ERROR] [PG::SyntaxError: ERROR:  zero-length delimited identifier at or near """"
  LINE 1: DELETE FROM "regions" WHERE "regions"."" = $1
  </code></pre>