Smallest commercially viable SQL database is probably the latest k5&#x2F;kdb (<a href="http:&#x2F;&#x2F;kparc.com&#x2F;" rel="nofollow">http:&#x2F;&#x2F;kparc.com&#x2F;</a>), which is implemented in something like 9KB of code (source: <a href="http:&#x2F;&#x2F;kparc.com&#x2F;o.htm" rel="nofollow">http:&#x2F;&#x2F;kparc.com&#x2F;o.htm</a>).