Re: problem with precendence order in JSONB merge operator

Subjective notes to contextualize (try to explain on bad-English) my
"precedence order" and JSONB visions:

JSON datatype is perfect as workaround, and for many simple and less
exigent applications.
JSONB is the "first class" datatype for user community, we expected years
(!) for it ... Need some "first class" and friendly behaviour.

In this context JSONB is not "any other" datatype, it is the bridge between
relational data and flexible data...
It is the Holy Grail and the Rosetta Stone :-)

I think JSONB operators need some more attention, in semantic and usability
contexts. If you want to add some friendliness and orthogonality in
JSONB operators, will be natural to see -> operator as a kind of
object-oriented *path* operator...
By other hand, of course, you can do the simplest to implement JSONB... But
you do a lot <http://www.postgresql.org/docs/9.5/static/functions-json.html>
(!), it was not easy to arrive here, and need only a little bit more
to reach perfection ;-)

2016-03-22 18:42 GMT-03:00 David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>:

> On Tue, Mar 22, 2016 at 1:52 PM, Peter Krauss <ppkrauss(at)gmail(dot)com> wrote:
>
>> Seems that parser not using precedence ideal order, and that casting
>> obligation losts performance.
>>
>> The first problem is self-evident in this example:
>>
>> SELECT '{"x":1}'::jsonb || (('{"A":{"y":2}}'::jsonb)->'A')
>> -- it is ok, expected result with (x,y)
>> SELECT '{"x":1}'::jsonb || '{"A":{"y":2}}'::jsonb)->'A'
>> -- non-expected result (y).
>>
>> Higher precedence <https://en.wikipedia.org/wiki/Order_of_operations> most
>> be for -> operator, that is like an object-oriented *path* operator,
>> always higher than algebric ones.
>>
> ​There is presently no formal concept of "path operator" in PostgreSQL.
> "->" is a user-defined operator, as is "||"​ and thus have equal
> precedence and left associativity.
>
> http://www.postgresql.org/docs/current/static/sql-syntax-lexical.html
>
> Regardless, "||" is not an "algebric" [sic] operator...I'm curious what
> source you are using to back your claim of operator precedence between
> different so-called "operator types".
>
> Its highly undesirable to make changes to operator precedence.
>
> Operators are simply symbols to the parser - there is no context involved
> that would allow making their precedence dynamic. So all PostgreSQL sees
> is "||", not a "JSONB merge operator".
>
> Other problem is using this operation as SQL function
>>
>> CREATE FUNCTION term_lib.junpack(jsonb,text) RETURNS JSONB AS $f$
>> SELECT ($1-$2)::JSONB || ($1->>$2)::JSONB;
>> $f$ LANGUAGE SQL IMMUTABLE;
>>
>> without casting produce error. Perhaps will be "more friendly" without
>> cast obligation,
>>
>> and it is a performance problem, the abusive use of castings losts
>> performance.
>>
> I cannot make this work...
>
> version
> PostgreSQL 9.5.1 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu
> 4.8.2-19ubuntu1) 4.8.2, 64-bit
>
> SELECT ('{"a":1,"b":2}'::jsonb - 'b'::text)::jsonb ||
> ('{"a":1,"b":2}'::jsonb #> 'b'::text)::jsonb
>
> > ​SQL Error: ERROR: invalid concatenation of jsonb objects
> ​
> This seems like user error but without a self-contained test case
> exercising the query (the use of a function in this context should be
> immaterial) I'm finding it hard to explain why. My simple case returns a
> non-object with rightly cannot be appended to an object.
>
> In isolatoin you can avoid casting the RHS of the || operator by using the
> "#>(jsonb,text[])" operator
>
> SELECT pg_typeof('{"a":1,"b":{"c":2}}'::jsonb #> array['b']::text[])
> --jsonb
>
> JSON, IME, still needs some fleshing out. Efficient usage might require
> additional features but for now one needs to get very familiar with all the
> various operator variants that allow the user to choose whether to return
> json or text and to pick the correct one for their needs.
>
> ​David J.
> ​
>
>