title: Count all rows and add a certain int from column of each result row into overall count
body: <p>I have a table consisting of columns tblEventID, isSafeSlot, plusOnes. I want to retrieve the number of rows where tblEventID is equal to <code>X</code> and isSafeSlot is equal to <code>true</code>, and if both are true, also check the column <code>plusOnes</code> for that one row. This column will hold an int from 0 to 99. I need to add those numbers also into the count.</p>
  <p>So say we have this table:</p>
  <pre class="lang-none prettyprint-override"><code>tblEventID / isSafeSlot / plusOnes
  100 / true / 0
  100 / true / 53
  100 / false / 0 
  101 / true / 99 
  </code></pre>
  <p>And I am giving it tblEventID 100, the count result should be 55 (two rows making the count 2, plus one row has the number 53 stored under <code>plusOnes</code>, result 55)</p>
  <p>How can I make this inside one query?</p>