ErwinSmout

Not necessarily.

If you ponder the importance of proper (robust, reliable, dependable) data management for data that keeps nuclear plants going, for farmaceutical research data, for anything happening on the financial markets, for medical records, for data concerning payroll and the like, etc. etc. then you might appreciate that all the stuff mentioned in the list is indeed really "just toys".

And Tony Hoare probably wished he hadn't made his "billion dollar mistake".

But at any rate, you could also try and ponder how unbelievably exceptionally awful it must have been that existed before SQL if something as truly awful as SQL could still be as successful as it has been.

SQL (the language that is, as defined by ISO) has COLLECT and UNNEST operators which come reasonably close (not 100% of course) to "Date's concept of relation-valued attributes". Moreover, I'm told those two operators are supported by at least one of the three big dogs.

"The one that his a lot of people is WHERE <value> NOT IN (<set>) where <set> contains a NULL. Because NOT IN unrolls to “<value> <> <s1> AND <value> <> <s2> AND … AND <value> <> <sx>” any NULL values in the set makes one predicate NULL which makes the whole expression NULL even if one or more of the other values match."

Sorry, but this is FALSE.

"Even if one of the other values match" will make that particular INequality test FALSE and one FALSE conjunct will make the entire conjunction FALSE, even in 3VL.

Yes. The reason is lazy people expect to be able to ask five questions in one go and expect one single answer to answer all five of them.

The key is to realize that submitting a query is to ask a question. So how many queries to you think you have to issue if the number of questions you have is five ?

It is technically perfectly possible to "ask five questions at the same time" to any given truly relational DBMS. Said DBMS will give five answers at the same time (and not leave you to guess which answer corresponds to which question). That SQL doesn't do it, does not mean it's impossible.

The predicate corresponding to an outer join is fundamentally disjunctive in nature (any outer join is equivalent to a UNION of at least 2 SELECTs) meaning that "after the fact", there is no way to determine which particular one of the disjuncts made the row appear in the result.

"Many of those complaints seem theoretical. I like to focus on practical concerns."

The only reason ever why people engage into theory, is precisely because of a deeply rooted desire to address "practical concerns". Hawking literally stated that his aim was to understand everything about the entire universe.

People who "like to focus on practical concerns" see an apple fall and (after they've seen it happen often enough and never ever otherwise) ultimately conclude that "apples fall and that's just how it is". Newton saw an apple fall and ultimately unveiled the concept of gravity. In doing so, Newton also unveiled the (admittedly extremely exceptional) circumstances in which it might be possible for us to see an apple "fall upward into the skies" after all.

:-)

And those that are built on "first principles" end up looking like a dog's breakfast just as well because people expect to not have to learn a novel language.

People don't want to be told to forget everything they thought they knew. People don"t want to be told they've been wrong for 40 yrs. Even if you add that it's not entirely their own fault because they've been consistently misled by an entire industry.

You can crack the problem of supporting CREATE ASSERTION, they'll still dismiss it (handwave handwave) believing you're just bluffing.

And I mostly disagree with the optimism built on Datalog.

"There were also definitely some bad paradigms invented as a result of SQL (e.g. all business logic lives in the database as stored procedures or stored functions),"

I hope you don't mean by that that integrity enforcement (checking the compliance of the data with ALL declared business rules) does not belong in the DBMS. Because the exact opposite is true : inside the DBMS is the only place where it belongs. Or if not the only, then certainly still the primary.

In the relational model, no there is no such thing as "optional values".

Even Codd often hinted (quite a bit of material in the 1990 book gives such hints) that "if a row has a null somewhere, it SHOULDN'T BE CONSIDERED AS BELONGING TO THE RELATION". E.g. if an attribute of a FK is null, no FK checking should be done at all on account of that null. The FK checking should be done only when the FK value is "complete".

As for outer join, one problem with it is that its result is (intended to be) the extension of a disjuctive predicate, the disjuncts in question being exactly the predicate for the "matching" case and the other one the predicate for the "no match" case. Now if you see a row in the result, how can you tell from that row which of the two disjuncts made that row appear in the result ?

Outer join is problematic by definition precisely because of the possibly ambiguous interpretation that derives from its disjunctive predicate.

(Would you do that with base tables ??? I mean design a base table that can hold a row for strictly more than one possible reason ??? I mean where the user then sees a row in that table and subsequently cannot tell whether that row is there for reason/meaning 1 or for reason/meaning 2 ??? I'll tell what you -and anyone else- would do in such a case : you'd also add the indicator telling whether it's meaning 1 or 2 (and then the problem of 'what if it's both' is also solved). Now think back about what could be done in outer join to resolve that very same kind of disjunctive ambiguity.)

"NULL only has one meaning: NULL. This is roughly analogous to unknown."

From the re-published version of "Much ado about nothing, part 2" (re-published in "Database Dreaming, Vol II) :

"An outer join produces nulls because we ask the DBMS to show us data from one table even when no matching data can be found in another table. Such nulls have no meaning, no semantic content."

Personally I'd add to that : and even if it's the case that they do, that meaning is patently not "simply unknown" but rather a very clear indication of non-existence.

But I have no doubt the apologists will obviously always apologize no matter what and handwave arguments such as these away with "So what ? What's the difference." Well, it's the difference between knowing of non-existence and not knowing at all.

In "Stating the obvious", C.J. Date wrote 50 (FIFTY) pages solely on the subject of how SQL screwed up with the most fundamental operator of all : testing for equality. I'll repeat : FIFTY pages about everything that SQL got wrong with just the equality operator.

Go figure about the rest ...

In fact, Date has recently revised a whole slew of "old" papers of his, got them up-to-date wrt his current thinking, and (re-) published them. His "A critique of SQL/86" paper(s) are now chapter 8, 9 & 10 of "Database Dreaming, Vol I" (there's a Vol II too).

What they "called out as flawed" was the impossibility to declare any such rule with SQL as it stood. What they were "criticizing" was precisely the fact that a data language that was supposed to be "expressively complete" was *unable* to express such a rule. You can't claim "expressive completeness" for a language if there is demonstrably a case where said language's expressiveness fails to meet the mark. It's not the "behaviour of the language" they were criticizing in all/any of those use cases that were supported by the language as it stood. They were criticizing the fact that there was a use case [and a relatively reasonable one on the face of it] that the language couldn't support.

Because "speaking SQL" [even before SQL as such was even invented, hence the scare quotes] was intended as a skill to be practiced only by those who also grasped the [mathematical] logic of what they were doing when "speaking SQL". None of the people who "speak SQL" these days fit that bill.

And FWIW, what I wrote was in reply to "mental model". It was *you* who apparently equated that with "speaking English". The "mental model" I described as "exactly the problem" is the "mental model" *of the corresponding logic*, which, though mathematically consistent, is hopelessly unintuitive. Being English-speaking or not has nothing to do with understanding a particular logic underpinning the behaviour of a particular Data Manipulation Language.