2016-11-13 18:13 GMT+01:00 Tom Lane <t...@sss.pgh.pa.us>: > Christian Convey <christian.con...@gmail.com> writes: > > * Our ultimate goal is to give Postgres an implementation of the > functions > > "JSON_EXISTS", "JSON_VALUE", and "JSON_QUERY" which fully comply with the > > SQL standards. > > * The best representation of those standards is found here: [1]. > > [1] > > http://jtc1sc32.org/doc/N2501-2550/32N2528-WG3-Tutorial- > Opening-Plenary.pdf > > You're going to need to find a draft standard somewhere, as that > presentation is too thin on details to support writing an actual > implementation. In particular, it's far from clear that this is > true at all: > > > * When [1] mentions a "JSON path expression" or "JSON path language", > it's > > referring to the query language described here: [2]. > > [2] http://goessner.net/articles/JsonPath > > The one slide they have on the path language mentions a lax/strict syntax > that I don't see either in the document you mention or in the Wikipedia > XPath article it links to. This does not give me a warm feeling. The SQL > committee is *fully* capable of inventing their own random path notation, > especially when there's no ISO-blessed precedent to bind them. > > In general, the stuff I see in these WG3 slides strikes me as pretty > horribly designed. The committee is evidently still stuck on the idea > that every feature they invent should have a bunch of new bespoke syntax > for function calls, which is a direction we really don't want to go in > because of the parser overhead and need for more fully-reserved keywords. > For instance: > WHERE JSON_EXISTS (T.J, 'strict $.where' FALSE ON ERROR) > Really? Who thought that was a better idea than a simple bool parameter? > > I have no objection to providing some functions that implement XPath-like > tests for JSON, but I'm not sure that you ought to try to tie it to > whatever the SQL committee is going to do, especially when they've not > published a finished standard yet. You may be chasing a moving target. > > As for whether JSONPath is the right spec to follow, I'm not sure. > The article you mention is from 2007 and I don't see all that many > other references in a Google search. I found this Wikipedia page: > https://en.wikipedia.org/wiki/Comparison_of_data_serialization_formats > which mentions half a dozen competitors, including "JSON Pointer" > which has at least gotten as far as being an RFC standard: > https://tools.ietf.org/html/rfc6901 > I'm not up enough on the JSON ecosystem to know which of these has the > most traction, but I'm unconvinced that it's JSONPath. >
We can use some other databases with this implementation as references. I have to agree, so the people in SQL committee are not too consistent - and sometimes creates too cobolish syntax, but it is standard - and it is implemented by major vendors. We doesn't need to implement full API - not in first step - important point is don't close door to possible ANSI conformance. In first step we can take the best and important from standard. It can be similar to our SQL/XML implementation - we implement maybe 75% - and only XPath instead XQuery, but I don't feel any weak. I see very useful "JSON_TABLE" function, which is good for start. Regards Pavel > regards, tom lane >
