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0 pointspurerandomness7y ago0 comments

SQL is a declarative language: You describe what you want, not how to get it.

If that's not what you need, there are plenty of procedural languages whith which you describe how to get things.

A query plan will change based on statistics. It's the engine's job to decide if your query is best served by parallelizing it to multiple cores, or deciding if it's worth JITing it before execution.

The actual execution of the query is an implementation detail of the engine, and should be. That's the entire point of a SQL standard: To provide users with an interface to talk to engines, which then retrieve the data you asked for.

It is its core strength and the reason why it's so successful.

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ebikelaw7y ago

"You describe what you want, not how to get it."

The entire archive of the pgsql users' mailing list disagrees. Every wants to know why their plan is suboptimal, or why it changed. People also want to know why the planner takes 100ms to generate the plan and only 1ms to execute the query, and so forth.

The idea that you just say what you want and you get the optimal result from your database is just ridiculous to anyone who has had to use them under any significant load.

mmt7y ago

> Every wants

This seems like mere selection bias.

As the sibling comment points out, users who have no problem aren't likely to post "Everything is fine!" to the mailing list. In fact, it would likely be rude to do so.

wvenable7y ago

The thing is, 99.999999% of the time (and I'm probably missing a few 9's) the engine does exactly the most optimal thing.

However, database engines aren't perfect -- I know I've encountered bugs in older SQL server versions where the query never finishes but making some trivial adjustments fixes it. This is a bug. And most mailing lists are filled with people encountering bugs. Saying what you want and getting the best result is exactly what you should expect.

zbentley7y ago

> The entire archive of the pgsql users' mailing list disagrees. Every wants to know why their plan is suboptimal, or why it changed.

And rather a lot of the archives of $scripting_language_of_your_choice are people confused about duck-typing/type system failures. That doesn't mean scripting languages should be replaced with statically typed ones; just that there are pain points in every system, and right (or wrong) tools for every job.

Don't believe me? Check how much of the FAQ traffic from first-time Rustaceans (or Swift/Java/etc. newcomers) has to do with how to satisfy their language's type system.

You pick your poison. SQL gives you a clearly defined set of tradeoffs up front. If that's not for you, no worries, move along.

zzzcpan7y ago

The biggest tradeoff SQL gives you is exactly the one GP points out: it's a leaky abstraction where understanding performance is tied to implementation so much, that you pretty much lose all the benefits of SQL, except familiarity with the technology.

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