Came here to post a summary but you did a better job than I could.<p><pre><code>   &gt; A few companies&#x2F;research groups are working on bridging 
   &gt; the gap between the extremes (unencrypted&#x2F;fully 
   &gt; homomorphic encryption) in order to come up with a good  
   &gt; compromise between security and cost.
</code></pre>
I just wanted to add that plain text vs homomorphic encryption is indeed a security and cost trade-off.<p>Fully vs partially homomorphic encryption is a trade-off between supported operations and cost. Fully homomorphic systems allow arbitrary computations while partially homomorphic systems do not, hence the lack of support for standard SQL.