title: Get first product ordered by customer
body: <p>I have an existing table like below. I want to replace the NULLs in first_product column with the first product a customer has ordered.</p>
  <p>INPUT</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>customer_id</th>
  <th>product</th>
  <th>order_date_id</th>
  <th>first_product</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>C0001</td>
  <td>apple</td>
  <td>20220224</td>
  <td>NULL</td>
  </tr>
  <tr>
  <td>C0001</td>
  <td>pear</td>
  <td>20220101</td>
  <td>NULL</td>
  </tr>
  <tr>
  <td>C0002</td>
  <td>strawberry</td>
  <td>20220224</td>
  <td>NULL</td>
  </tr>
  <tr>
  <td>C0001</td>
  <td>apple</td>
  <td>20220206</td>
  <td>NULL</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>OUTPUT:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>customer_id</th>
  <th>product</th>
  <th>order_date_id</th>
  <th>first_product</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>C0001</td>
  <td>apple</td>
  <td>20220224</td>
  <td>pear</td>
  </tr>
  <tr>
  <td>C0001</td>
  <td>pear</td>
  <td>20220101</td>
  <td>pear</td>
  </tr>
  <tr>
  <td>C0002</td>
  <td>strawberry</td>
  <td>20220224</td>
  <td>strawberry</td>
  </tr>
  <tr>
  <td>C0001</td>
  <td>apple</td>
  <td>20220206</td>
  <td>pear</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I have thought about using row numbers as below, but not sure how to pull it all together.
  I have this code so far, but not sure how to update the first_product column using the below code.</p>
  <pre class="lang-sql prettyprint-override"><code>ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY customer_id, order_date_id) AS first_occurrance
  </code></pre>
  <p>Some pseudo-code:</p>
  <pre><code>REPLACE first_product FROM table WITH product WHERE
  ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY customer_id, order_date_id) AS first_occurrance =  1 
  </code></pre>