Simply, it is an adapter that lets you use SQL syntax to introspect Ethereum blockchain data (blocks, and transactions.) Typically people do this using a JS API built into the node software , and it may/may not be ones' cup of tea.
As I've pointed out before, smart contracts need atomic transactions. Either everything commits, or nothing commits. This is a basic property needed for accounting systems.
There's one well-known exception, which is that if your contract sends ETH to another contract, invoking its fallback function, then a throw in the callee just means the call returns false. So in that particular case you have to check the return value and rethrow to make it atomic; this sounds crazy but in some circumstances you don't actually want to throw. The compiler gives you a warning if you don't check.
What I would instead wager is that it's too easy to introduce reentrant errors in Solidity.
I've noticed since the DAO exploit, the ecosystem has been better about this though. For example, Solidity's docs has a section of reentrancy, and even the in-browser editor can warn you about reentrancy in some cases. Seems to be improving, though unfortunately after big expense.
It's sometimes easy to miss, but the ecosystem is also a lot better at insisting on public security audits.
(insert "should i use a blockchain" infographic, which is amusingly impossible to google image search for, because this question evidently does not often occur to people...)
"get used to blockchain when all you know is SQL" - cool.
"guarantee all us non-trusted nodes have the same SQL database" - ...sure, but for any project such that i want this, i'm pretty sure i don't need a blockchain. (but of course, your project doubtless has uses i haven't thought of)
"i want a trustless SQL database so i'm going to use EVM and solidity and put it on The Blockchain because i'm awesome" - very bad.
"i'm starting a new project, so naturally i need to use a blockchain" - extremely bad.
Presto itself has a JDBC driver, so you could run it + this plugin in a Java app/codebase
Edit: Sorry for the negativity. I created a PR for it. https://github.com/xiaoyao1991/presto-ethereum/pull/8
Nope, still not putting money/time here, sorry.