Is it safe to use SUM() without ISNULL()
<p>I am trying to hence the performance of an SP. I have a doubt in my mind about SUM and ISNULL. When I sum up a column, should I use ISNULL? Is it SAFE to use SUM() without ISNULL. My example is below</p>

<pre><code>SUM(ISNULL(COL1,0))
</code></pre>

<p>Since ISNULL costs a lot, I intend to use SUM without ISNULL like below</p>

<pre><code>SUM(COL1)
</code></pre>

<p>I did some small tests and I couldnt see results</p>