That's probably why many of the libraries mentioned in this thread use "smoke and mirrors". Of course, it is quite possible to correctly escape a value by rendering it to a string first, _then_ encoding the whole thing.
To have true parameterised queries, you need to use the "binary" protocol, which many MySQL libraries don't offer support for. (MySQL also has some frustrating limitations with the binary protocol, such as not allowing a SQL string containing more than one statement to be prepared.)
Do you have examples of libraries that's actually a "parametrized query"? The python libraries I encountered (psycopg2, sqlalchemy) both seem to be "fake smoke and mirrors".
They are seemingly run through a stored procedure on the server side, with each parameter passed in as an argument. This has some consequences that lead to very obscure behavior, too [1].
For example, you should never create temporary tables in an SQL statement that was initialized with parameters, as they won't survive the end o the statement; they will be destroyed as soon as the innermost scope (within the stored procedure call) finishes.
I ran into this because I tried setting up a single "run this query" method in a more complicated database routine in order to keep my C# code clean... didn't work out as I'd hoped ;)
[1]: https://stackoverflow.com/a/46311328
Edit: I just realized that this still isn't a guarantee that parameters are handled as a separate structure by the underlying network protocol. I hope they are -- but I don't know how to check. Maybe the according .NET Core code is on GitHub?
Every MySQL client needs to do something similar, due to the design of the MySQL protocol.
Eek. "select * from classes where teacher = '?'" -> boom.
https://github.com/WordPress/WordPress/blob/4ae0744585ea9417...
They do seem to have resisted attacks for quite a while though.
Except there is no such thing as "actual parametrized queries", either as defined by the SQL standard or as supported by any of the major RDBMS vendors.
The closest thing we have are prepared statements, which are basically session-scoped stored procedures used by client-side libraries to pull off the illusion of parametrized queries.
I wouldn't be surprised that if you go back far enough, the idea of parametrized queries probably started in client libraries trying solve for SQL string soup with a dash of sprintf-like syntax sugar.
In the sense that stored procedures and prepared statements are queries, sure. But your SQL statement and your values are not being sent in the same call to the database.
That would surprise me... I thought that when I send a parameterized query to PostgreSQL or MS SQL Server, most (or even all) of the query plan gets created without looking at any parameter values. And if that is true, then I think your "no such thing" claim cannot be true. If the query plan has already been created based on the unparameterized SQL string, then parameter values cannot cause it to do something crazy like drop an unrelated table.
(But I haven't read the source code to either of those RDBMS, so maybe I am about to be surprised.)
Your comment peaked my interest so I looked into what postgres does, and it's pretty ingenious in my opinion. It can create either a generic plan (not looking at parameter values) or a custom plan where it looks at parameter values and then uses statistics to find the best plan.
By default, for the first 5 executions of a prepared statement uses a custom plan. If the execution costs of these different plans are pretty close to each other, from then on it just uses the generic plan (idea being that the extra cost of generating a custom plan each time isn't worth it), but if they are different enough (meaning looking at statistics can have a big speedup), then custom plans are used going forward. This behavior can be tweaked using DB flags.
You're not sending a parameterized query. The libraries are creating prepared statements under the hood, and managing them for you. This generally requires one call to prepare the statement and fetch some sort of handle, and then executing the statement with the handle from the first call.
Part of the confusion is that it's common to see SQL libraries offer an API to parametrize queries using some sort of placeholder in the query, but it's really just a facade to perform local string interpolation along with some sort of vendor-specific sanitation scheme.
Not always. The Node `pg` module pipelines down the commands on the connection: it sends a `prepare` command, then a `bind` command, then an `execute` command. Yes, it uses prepared statements under the hood, but there is no wire round trip between prepare and bind.
We're in the process of adding support for MSSQL in addition to the DB server we've been using for ages. This is one of the pain points. They differ in how they handle "parameterized queries" enough to be a PITA.
Is this really possible if the server considers table statistics (i.e. frequencies of certain values) when forming a plan?
And still much preferable to not having it at all.
Don’t let perfect be the enemy of good.
The alternative for people using a library like this is to send plain queries to the db.
/s/today/30 years ago: SQL-92 describes them in chapter 4.18 - which at the time was just standardizing something almost all vendors already had in some form or another, for example, I'm pretty sure even the first release of ODBC in the late 1980s also had parameters.
Disclaimer: My pontifications below derive from my life's experiences starting with Access/JET Red as a sprog, to my current professional work with MS SQL Server, Postgres (and MySQL, I'll admit - but I'll say MariaDB instead) built over the past 17 years - but I have absolutely zero experience with Oracle and Db2, so I honestly don't know what cool language features they have (and they must be way ahead of the ISO spec, otherwise why else would people pay so much for it?... Hmm, then again, Oracle still doesn't have a bit/bool column type, does it?).
Anyway:
However, the expressiveness of parameters hasn't changed much since the original design of ODBCS - at least as far as I'm aware: Query parameters are still mere scalar value placeholders instead of hardcoding literals inside queries and statements: with limited exceptions like T-SQL's ceremony-laden table-valued-parameters and Postgre's array types, it's still not possible to parameterize database object identifiers or even have a true variadic `WHERE IN ( ... )` predicate without resorting to Dynamic-SQL, nor can we use parameters to conditionally enable or disable query predicate clauses: yet these are all essential features for any kind of ORM or language-integrated-query system built today (the canonical example being Linq/EF in .NET and TypeORM or Prisma for TypeScript/JS.
Why isn't anyone meaningfully advocating for a "SQL/2"? I know backwards-compatibility is 100% essential, but that's the easy part (because relational calculus and relational are isomorphisms, hence why semantic-preserving query translation between different SQL engines is a solved problem), but lack-of backwards-compatibility is usually the reason most good-ideas die in committee - so how come Google was successful in pushing HTTP/2 and even HTTP/3, but we're still using 1980s-level SMTP and SQL? Are all of the major RDBMS vendors so afraid of change that they're willing to forgoe winning-over millions of new customers if they can ship a usable, flexible, expressive, and safe query (and query-building) language?
I'm just blabbering at this point. Forgive me, but I need something to distract me from the outside world right now.
Interbase must have had them in 1980s since Interbase (and now Firebird) compiles ESQL queries into static BLR code. Since there's no way to compile a new query at runtime (other than by outright switching to using Interbase/Firebird's DSQL C API for a non-compile-time query), all these queries have to be parameterized to be of any use.
Their description of BLR makes it sound like an eagerly-evaluated equivalent of SQL Server’s Execution Plans, but are compiled on CREATE instead of on first-use, and are comprised of machine-native (i.e. raw x86/x64 + disk read syscalls) operators arranged together - or maybe slightly higher-level? It’s unclear how schema-binding works.
I’m curious what advantages there are to that approach anymore: databases are invariably IO-bound, not CPU bound, and things like well-maintained indexes and statistics objects are far more important when it comes to DB perf than the ISA of the query engine. I’d wager an ultramodern engine running in WASM or even interpreted Java will run faster on the same hardware than JET, I’d think.
On a related note, why are we still stuck with 4K/8K-sized pages?
Obviously they’ve been proven for tens of years now, so it’s extremely unlikely, but conceptually it isn’t different.
Parametrized Queries for a SQL library are a critical “do not ship without” feature. You do not lie and tell your user you have a safe product causing them to have a compromised system.
I hope to God you are not creating production systems anywhere.
I don't understand how anyone but the greenest of devs doesn't comprehend the importance of these kind of things. But alas, I see it everywhere, including the comment you are responding to.
I ask about SQL injection pretty regularly, and it's scary how many devs don't seem to even know what it is.
That's either a good thing: because they grew-up with database libraries designed to encourage, if not force, the use of parameterized queries, so it was never a problem for them.
...or it's a bad thing, because they grew-up in the early-days of PHP 4x, learning from PHP/MySQL tutorials written by people who'd today be considered utterly unqualified to speak at length about programming: the kinds of things that only happen when the blind were leading the blindfolded: nightmares like actively encouraging concatenating $_GET values directly into mysql_query() strings because it means having less variables, and less variables means better performance (right?!) - and they never learned otherwise.
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I have a pet theory that people who got started with PHP in the 2000s who are still working today are so burned from their earlier experiences that they're now the most detail-oriented and best-practices-following programmers around, regardless of the language they use today - while the people who never experienced hardship (to the extent that having to use PHP is a hardship...) become complacent, and our ever-increasing reliance on unvetted external dependencies (in all language ecosystems, imo) is going to end badly.
Or not. No idea, honestly!
Good luck building production systems without compromises.
Also, I think everyone would appreciate it if you didn’t hurl personal insults about. This aint Reddit.