title: Join 3 tables using ecto query
body: <p>Here is a scenario with <a href="https://arstechnica.com/civis/viewtopic.php?f=20&amp;t=763512" rel="nofollow noreferrer">Postgres</a> </p>
  
  <pre><code>CREATE TABLE "hearings" (
    "hearing_id" int4 NOT NULL,
    "date" timestamp NOT NULL,
    "time" varchar(32),
    "committee" varchar(255),
    "summary" text,
  );
  
  
  CREATE TABLE "categories" (
    "category_id" int4 NOT NULL,
    "description" varchar(255) NOT NULL,
    "type" varchar(32) DEFAULT 'normal' NOT NULL,
  );
  
  
  CREATE TABLE "hearing_category_link" (
    "hearing_id" int4 NOT NULL,
    "category_id" int4 NOT NULL,
  );
  </code></pre>
  
  <p>Postgres query:</p>
  
  <pre><code>SELECT * FROM
  (hearings LEFT JOIN hearing_category_link ON hearings.hearing_id = hearing_category_link.hearing_id )
  LEFT JOIN categories ON hearing_category_link.category_id = categories.category_id
  </code></pre>
  
  <p>So far I am only able to join current query with one table </p>
  
  <pre><code>from h in "hearings", join: hl in "hearing_category_link", on: hl.hearing_id == h.hearing_id
  </code></pre>
  
  <p>But I want to join these 3 tables using ecto and get the results(dynamically would be awesome). <a href="https://stackoverflow.com/questions/15799556/postgresql-join-data-from-3-tables">Another similar question but with postgres</a></p>