_If we aren’t matching the feature, why are we matching the keyword?_ ??? Nobody said that if we do not use the exact same feature we have to rename it.
On Fri, Apr 11, 2025 at 6:13 PM Benedict <bened...@apache.org> wrote: > [image: elephant.png] > > 5.5. Constraints > <https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-CHECK-CONSTRAINTS> > postgresql.org > <https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-CHECK-CONSTRAINTS> > > <https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-CHECK-CONSTRAINTS> > > > See the note directly above section 5.5.2 - Postgres supports functions in > the CHECK predicate and requires they are pure functions (ie always yield > the same result). > > The point is, CHECK is consistently a predicate defined over a field > expression. If we aren’t matching the feature, why are we matching the > keyword? > > I also disagree that CHECK is a useful prefix to all constraints, and > would prefer consistency with Postgres here that also uses plain NOT NULL > for a NOT NULL constraint. > > > On 11 Apr 2025, at 17:05, Štefan Miklošovič <smikloso...@apache.org> > wrote: > > > I went through Postgres' docs in a quite elaborate manner and I do not see > any usage of "constraint functions" as we have them. Both MySQL and > Postgres seem to only provide simple predicates (using relational > operators) and "functions" as we have them (e.g. json / length) are not > supported. So in this regard we are providing more than they do. Where have > you taken "is_json(field)" form from? Not saying it's wrong, I am just > curious where this is coming from. > > I do not like that we would have "NOT NULL" without "CHECK". I think we > can go a little bit our own way as we have the comfort of modelling this > from scratch. CQL is already different from SQL as is and I do not think > that trying to follow SQL _orthodoxly_ is absolutely necessary but at the > same time I find it easier and more welcoming for users coming to Cassandra > for the first time to have syntax which is as close as possible to what > they are used to. > > I find having constraints starting with "CHECK" _every time_ consistent. > They do not need to think twice if "check" is going to be there or not. It > is there every time. I do not know why SQL did not do it the same way, most > probably because "NOT NULL" was the first being introduced and "CHECK" > followed afterwards and it was just too late to it consistent. > > > > On Fri, Apr 11, 2025 at 5:33 PM Bernardo Botella < > conta...@bernardobotella.com> wrote: > >> Benedict: >> >> An alternative for that, keeping the CHECK word, would be to change the >> constraint name to IS_JSON. CHECK IS_JSON would read as you intend without >> the need to jump to REQUIRE. I think that’s true for the rest of provided >> constraints as well. >> >> Bernardo >> >> >> On Apr 11, 2025, at 6:02 AM, Benedict <bened...@apache.org> wrote: >> >> We have taken a different approach though, as we do not actually take a >> predicate on the RHS and do not supply the column name. In our examples we >> had eg CHECK JSON, which doesn’t parse unambiguously to a human. The >> equivalent to Postgres would seem to be CHECK is_json(field). >> >> I’m all for following an existing example, but once we decide to diverge >> the justification is gone and we should decide holistically what we think >> is best. So if we want to elide the column entirely and have a list of >> built in restrictions, I’d prefer eg REQUIRE JSON since this parses >> unambiguously to a human, whereas if we want to follow Postgres let’s do >> that but do it but that means eg CHECK is_json(field). >> >> On 11 Apr 2025, at 10:57, Štefan Miklošovič <smikloso...@apache.org> >> wrote: >> >> >> While modelling that, we followed how it is done in SQL world, PostgreSQL >> as well as MySQL both use CHECK. >> >> >> https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-CHECK-CONSTRAINTS >> >> https://dev.mysql.com/doc/refman/8.4/en/create-table-check-constraints.html >> >> On Fri, Apr 11, 2025 at 10:43 AM Benedict <bened...@apache.org> wrote: >> >>> I would prefer require/expect/is over check >>> >>> On 11 Apr 2025, at 08:05, Štefan Miklošovič <smikloso...@apache.org> >>> wrote: >>> >>> >>> Yes, you will have it like that :) Thank you for this idea. Great >>> example of cooperation over diverse domains. >>> >>> On Fri, Apr 11, 2025 at 12:29 AM David Capwell <dcapw...@apple.com> >>> wrote: >>> >>>> I am biased but I do prefer >>>> >>>> val3 text CHECK NOT NULL AND JSON AND LENGTH() < 1024 >>>> >>>> Here is a similar accord CQL >>>> >>>> BEGIN TRANSACTION >>>> LET a = (…); >>>> IF a IS NOT NULL >>>> AND a.b IS NOT NULL >>>> AND a.c IS NULL; THEN >>>> — profit >>>> END IF >>>> COMMIT TRANSACTION >>>> >>>> On Apr 10, 2025, at 8:46 AM, Yifan Cai <yc25c...@gmail.com> wrote: >>>> >>>> Re: reserved keywords, “check” is currently not, and I don’t think it >>>> needs to be a reserved keyword with the proposal. >>>> >>>> ------------------------------ >>>> *From:* C. Scott Andreas <sc...@paradoxica.net> >>>> *Sent:* Thursday, April 10, 2025 7:59:35 AM >>>> *To:* dev@cassandra.apache.org <dev@cassandra.apache.org> >>>> *Cc:* dev@cassandra.apache.org <dev@cassandra.apache.org> >>>> *Subject:* Re: Constraint's "not null" alignment with transactions and >>>> their simplification >>>> >>>> If the proposal does not introduce “check” as a reserved keyword that >>>> would require quoting in existing DDL/DML, this concern doesn’t apply and >>>> the email below can be ignored. This might be the case if “CHECK NOT NULL” >>>> is the full token introduced rather than “CHECK” separately from >>>> constraints that are checked. >>>> >>>> If “check” is introduced as a standalone reserved keyword: my primary >>>> feedback is on the introduction of reserved words in the CQL grammar that >>>> may affect compatibility of existing schemas. >>>> >>>> In the Cassandra 3.x series, several new CQL reserved words were added >>>> (more than necessary) and subsequently backed out, because it required >>>> users to begin quoting schemas and introduced incompatibility between 3.x >>>> and 4.x for queries and DDL that “just worked” before. >>>> >>>> The word “check” is used in many domains (test/evaluation engineering, >>>> finance, business processes, etc) and is likely to be used in user schemas. >>>> If the proposal introduces this as a reserved word that would require it to >>>> be quoted if used in table or column names, this will create >>>> incompatibility for existing user queries on upgrade. >>>> >>>> Otherwise, ignore me. :) >>>> >>>> Thanks, >>>> >>>> – Scott >>>> >>>> ––– >>>> Mobile >>>> >>>> On Apr 10, 2025, at 7:47 AM, Jon Haddad <j...@rustyrazorblade.com> >>>> wrote: >>>> >>>> >>>> This looks like a really nice improvement to me. >>>> >>>> >>>> On Thu, Apr 10, 2025 at 7:27 AM Štefan Miklošovič < >>>> smikloso...@apache.org> wrote: >>>> >>>> Recently, David Capwell was commenting on constraints in one of Slack >>>> threads (1) in dev channel and he suggested that the current form of "not >>>> null" constraint we have right now in place, e.g like this >>>> >>>> create table ks.tb (id int primary key, val int check not_null(val)); >>>> >>>> could be instead of that form used like this: >>>> >>>> create table ks.tb (id int primary key, val int check not null); >>>> >>>> That is - without the name of a column in the constraint's argument. >>>> The reasoning behind that was that it is not only easier to read but there >>>> is also this concept in transactions (cep-15) where there is also "not >>>> null" used in some fashion and it would be nice if this was aligned so a >>>> user does not encounter two usages of "not null"-s which are written down >>>> differently, syntax-wise. >>>> >>>> Could the usage of "not null" in transactions be confirmed? >>>> >>>> This rather innocent suggestion brought an idea to us that constraints >>>> could be quite simplified when it comes to their syntax, consider this: >>>> >>>> val int check not_null(val) >>>> val text check json(val) >>>> val text check lenght(val) < 1000 >>>> >>>> to be used like this: >>>> >>>> val int check not null >>>> val text check json >>>> val text check length() < 1000 >>>> >>>> more involved checks like this: >>>> >>>> val text check not_null(val) and json(val) and length(val) < 1000 >>>> >>>> might be just simplified to: >>>> >>>> val text check not null and json and length() < 1000 >>>> >>>> It almost reads like plain English. Isn't this just easier for an eye? >>>> >>>> The reason we kept the column names in constraint definitions is that, >>>> frankly speaking, we just did not know any better at the time it was about >>>> to be implemented. It is a little bit more tricky to be able to use it >>>> without column names because in Parser.g / Antlr we just bound the grammar >>>> around constraints to a column name directly there. When column names are >>>> not going to be there anymore, we need to bind it later in the code behind >>>> the parser in server code. It is doable, it was just about being a little >>>> bit more involved there. >>>> >>>> Also, one reason to keep the name of a column was that we might specify >>>> different columns in a constraint from a column that is defined on to have >>>> cross-column constraints but we abandoned this idea altogether for other >>>> reasons which rendered the occurrence of a column name in a constraint >>>> definition redundant. >>>> >>>> To have some overview of what would be possible to do with this >>>> proposal: >>>> >>>> val3 text CHECK SOMECONSTRAINT('a'); >>>> val3 text CHECK JSON; >>>> val3 text CHECK SOMECONSTRAINT('a') > 1; >>>> val3 text CHECK SOMECONSTRAINT('a', 'b', 'c') > 1; >>>> val3 text CHECK JSON AND LENGTH() < 600; >>>> afternoon time CHECK afternoon >= '12:00:00' AND afternoon =< >>>> '23:59:59'; >>>> val3 text CHECK NOT NULL AND JSON AND LENGTH() < 1024 >>>> >>>> In addition to the specification of constraints without columns, what >>>> would be possible to do is to also specify arguments to constraints. It is >>>> currently not possible and there is no constraint which would accept >>>> arguments to its function but I think that to be as flexible as possible >>>> and prepare for the future, we might implement it as well. >>>> >>>> Constraints in their current form are already usable however I just >>>> think that if we do not simplify, align and extend the syntax right now, >>>> before it is baked in in a release, then we will never do it as it will be >>>> quite tricky to extend this without breaking it and maintaining two >>>> grammars at the same time would be very complex if not flat out impossible. >>>> >>>> Are you open to the simplification of constraint definitions as >>>> suggested and what is your feedback about that? I already have a working >>>> POC which just needs to be polished and tests fixed to accommodate the new >>>> approach. >>>> >>>> Regards >>>> >>>> (1) https://the-asf.slack.com/archives/CK23JSY2K/p1742409054164389 >>>> >>>> >>>> >>
