Re: SQL/JSON query functions context_item doc entry and type requirement

On Thu, Jun 20, 2024 at 5:46 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
>
> On Thu, Jun 20, 2024 at 1:03 AM David G. Johnston
> <david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
> > On Wed, Jun 19, 2024 at 8:29 AM jian he <jian(dot)universality(at)gmail(dot)com> wrote:
> >>
> >> On Mon, Jun 17, 2024 at 9:05 PM Chapman Flack <jcflack(at)acm(dot)org> wrote:
> >> >
> >> > Hi,
> >> >
> >> > On 06/17/24 02:43, Amit Langote wrote:
> >> > > <replaceable>context_item</replaceable> expression can be a value of
> >> > > any type that can be cast to <type>jsonb</type>. This includes types
> >> > > such as <type>char</type>, <type>text</type>, <type>bpchar</type>,
> >> > > <type>character varying</type>, and <type>bytea</type> (with
> >> > > <code>ENCODING UTF8</code>), as well as any domains over these types.
> >> >
> >> > Reading this message in conjunction with [0] makes me think that we are
> >> > really talking about a function that takes a first parameter of type jsonb,
> >> > and behaves exactly that way (so any cast required is applied by the system
> >> > ahead of the call). Under those conditions, this seems like an unusual
> >> > sentence to add in the docs, at least until we have also documented that
> >> > tan's argument can be of any type that can be cast to double precision.
> >> >
> >>
> >> I guess it would be fine to add an unusual sentence to the docs.
> >>
> >> imagine a function: array_avg(anyarray) returns anyelement.
> >> array_avg calculate an array's elements's avg. like
> >> array('{1,2,3}'::int[]) returns 2.
> >> but array_avg won't make sense if the input argument is a date array.
> >> so mentioning in the doc: array_avg can accept anyarray, but anyarray
> >> cannot date array.
> >> seems ok.
> >
> >
> > There is existing wording for this:
> >
> > "The expression can be of any JSON type, any character string type, or bytea in UTF8 encoding."
> >
> > If you add this sentence to the paragraph the link that already exists, which simply points the reader to this sentence, becomes redundant and should be removed.
>
> I've just posted a patch in the other thread [1] to restrict
> context_item to be of jsonb type, which users would need to ensure by
> adding an explicit cast if needed. I think that makes this
> clarification unnecessary.
>
> > As for table 9.16.3 - it is unwieldy already. Lets try and make the core syntax shorter, not longer. We already have precedence in the subsequent json_table section - give each major clause item a name then below the table define the syntax and meaning for those names. Unlike in that section - which probably should be modified too - context_item should have its own description line.
>
> I had posted a patch a little while ago at [1] to render the syntax a
> bit differently with each function getting its own syntax synopsis.
> Resending it here; have addressed Jian He's comments.
>
> --

@@ -18746,6 +18752,7 @@ ERROR: jsonpath array subscript is out of bounds
<literal>PASSING</literal> <replaceable>value</replaceable>s.
</para>
<para>
+ Returns the result of applying the SQL/JSON
If the path expression returns multiple SQL/JSON items, it might be
necessary to wrap the result using the <literal>WITH WRAPPER</literal>
clause to make it a valid JSON string. If the wrapper is

+ Returns the result of applying the SQL/JSON
is redundant?

playing around with it.
found some minor issues:

json_exists allow: DEFAULT expression ON ERROR, which is not
mentioned in the doc.
for example:
select JSON_EXISTS(jsonb '{"a": [1,2,3]}', 'strict $.a[5]' default
true ON ERROR);
select JSON_EXISTS(jsonb '{"a": [1,2,3]}', 'strict $.a[5]' default 0 ON ERROR);
select JSON_EXISTS(jsonb '{"a": [1,2,3]}', 'strict $.a[5]' default 11 ON ERROR);

JSON_VALUE on error, on empty semantics should be the same as json_query.
like:
[ { ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } | DEFAULT expression }
ON EMPTY ]
[ { ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } | DEFAULT expression }
ON ERROR ])

examples:
select JSON_value(jsonb '[]' , '$' empty array on error);
select JSON_value(jsonb '[]' , '$' empty object on error);