How to sum the data in a row in SQL Server?
<p>I have a table with sample like this:</p>

<p><a href="https://i.stack.imgur.com/zAYbD.png" rel="nofollow"><img src="https://i.stack.imgur.com/zAYbD.png" alt="enter image description here"></a></p>

<p>In this example there are Day1, Day2, and Day3 but in the real data it could be Day1 through Day100.</p>

<p>How can I sum the data in the row for a particular range like Day1 through Day3 or Day2 through Day10 for TSTID = 1?</p>