title: Rails Activerecord Relation: using subquery as a table for a SQL select statement
body: <p>Can somebody help me figure out how to write the following SQL using Rails (I'm using Rails 4) Activerecord methods?  I know you can do this with find_by_sql but I'd like to preserve the active record relation.  Here's the sql for a postGreSQL db that I'm trying to create:</p>
  
  <pre><code>SELECT * FROM 
  (SELECT DISTINCT ON(table_a.id) table_a.name as alias_a, table_b.id, table_b.time
  FROM table_1
  LEFT OUTER JOIN table_b ON table_a.id = table_b.id
  ORDER BY table_a.id, table_b.time asc) AS subquery
  ORDER BY alias_a asc
  </code></pre>
  
  <p>For my subquery, I have the following (which generates the sql of the subquery above):</p>
  
  <pre><code>@subquery = table_a.select("DISTINCT ON(table_a.id) table_a.name as alias_a, table_b.time")     
  @subquery = @subquery.joins("LEFT OUTER JOIN table_b ON table_a.id = table_b.id")
  @subquery = @subquery.order("table_a.id, table_b.time asc")
  </code></pre>
  
  <p>But, I can't figure out how to write a select statement that uses @subquery as the table for the outer select statement.</p>