Re: SQL/JSON path issues/questions

On Fri, Jun 28, 2019 at 8:10 AM Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
>
> On 2019-Jun-28, Alexander Korotkov wrote:
>
> > On Tue, Jun 25, 2019 at 6:38 PM Liudmila Mantrova
> > <l(dot)mantrova(at)postgrespro(dot)ru> wrote:
> > > Thank you for the catch! Please see the modified version of patch 0004
> > > attached.
> >
> > I tried to review and revise the part related to filters, but I failed
> > because I don't understand the notions used in the documentation.
> >
> > What is the difference between filter expression and filter condition?
> > I can guess that filter expression contains question mark,
> > parentheses and filter condition inside. But this sentence is in
> > contradiction with my guess: "A filter expression must be enclosed in
> > parentheses and preceded by a question mark". So, filter expression
> > is inside the parentheses. Then what is filter condition? The same?
>
> The SQL standard defines "JSON filter expressions" (in 9.39 of the 2016
> edition). It does not use either term "filter condition" nor bare
> "filter"; it uses "JSON path predicate" which is the part of the JSON
> filter expression that is preceded by the question mark and enclosed by
> parens.

Yes, this is what I used in my talk
http://www.sai.msu.su/~megera/postgres/talks/jsonpath-ibiza-2019.pdf

>
> Maybe we should stick with the standard terminology ...

Sure.

As for the jsonpath documentation, I think we should remember, that
jsonpath is a part of SQL/JSON, and in the following releases we will
expand documentation to include SQL/JSON functions, so I suggest to
have one chapter SQL/JSON with following structure:
1. Introduction
1.1 SQL/JSON data model
1.2 SQL/JSON path language
1.3 <SQL/JSON functions> -- to be added
2. PostgreSQL implementation
2.1 jsonpath data type -- link from json data types
2.2 jsonpath functions and operators -- link from functions
2.3 Indexing

I plan to work on a separate chapter "JSON handling in PostgreSQL" for
PG13, which includes
JSON(b) data types, functions, indexing and SQL/JSON.

>
> --
> Álvaro Herrera https://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>
>

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