title: Finding sum and grouping in sequelize
body: <p>I have a donations table as follows.</p>
  
  <p><strong>Donations Table</strong></p>
  
  <pre><code>| id| amount | member_id |
  |---|--------|-----------|
  | 0 |   500  |         01|
  | 1 |  1000  |         02|
  | 2 |  2000  |         01|
  </code></pre>
  
  <p>How to find sum and group the table by member id as follows.</p>
  
  <pre><code>| amount | member_id |
  |--------|-----------|
  |  2500  |         01|
  |  1000  |         02|
  </code></pre>
  
  <p>I tried to use the following code but it doesnt seem to work.</p>
  
  <pre><code>const salesValue = await DONATIONS.sum('amount', {
      group: 'member_id'
  });
  </code></pre>