Join & Subquery to calculate Minimum datediff
<p>I have 2 SQL tables, one for <code>subscribers (ID, Name)</code>, second for <code>subscribers_Upgrades [Subscriber_ID (FK), Upgrade_Level, Upgrade_Date)</code></p>

<p>(There are 7 upgrade levels)</p>

<p>I need a query to get the top 10 subscribers who upgraded in the shortest period and <code>Upgrade_Level</code>, and <code>Upgrade Date</code> for specific <code>Upgrade_Level</code> (any one of the available 7 Upgrade level), and within specific period of time</p>

<p>We can, for example supply the 2 conditions like<br>
<code>Where Upgrade_Level = 3 and Upgrade_Date between '01-April-2014' and '20-May-2016'</code></p>