title: I want to aggregate data each same date
body: <p>I want to aggregate data each same date.
  I wrote SQL in BigQuery.
  Now there is a table like </p>
  
  <pre><code>id | date                  | country | code
  1    2015-10-16T12:00:30     Japan     A
  2    2015-10-16T12:00:30     America   C
  3    2017-08-20T15:50:44     America   B
  4    2016-22-56T11:32:01     China     E
  5    2017-08-20T15:50:44     EU        D
  </code></pre>
  
  <p>I want to change upper tabble into this</p>
  
  <pre><code>
  id    | date                  | country       | code
  1,2    2015-10-16T12:00:30     Japan,America    A,C
  3,5    2017-08-20T15:50:44     America,EU       B,D
  4      2016-22-56T11:32:01     China            E
  </code></pre>
  
  <p>It is like  put together id・country・code in each date.</p>
  
  <p>How should I write query to do this?</p>