Hi, Sergey. To me the XPath version seems correct here. So both we and MySQL are wrong. Though the JSON_Extract function is the MySQL-s invention so it's tempting to make it working like they do. So i'm in doubt how to fix this.
A. On Fri, Nov 20, 2020 at 12:18 AM Sergey Petrunia <[email protected]> wrote: > Hi Alexey, > > I've found this discrepancy in JSONPath evaluation: > > > set @json_doc3 = > ' > { > "root": { > "child1" : { > "child2" : { > "child1" : { > "x":124 > } > } > } > } > } > '; > > select json_extract(@json_doc3, '$**.child1**.x'); > > MariaDB [test]> select json_extract(@json_doc3, '$**.child1**.x'); > +--------------------------------------------+ > | json_extract(@json_doc3, '$**.child1**.x') | > +--------------------------------------------+ > | NULL | > +--------------------------------------------+ > 1 row in set (0.001 sec) > > MySQL-8> select json_extract(@json_doc3, '$**.child1**.x'); > +--------------------------------------------+ > | json_extract(@json_doc3, '$**.child1**.x') | > +--------------------------------------------+ > | [124] | > +--------------------------------------------+ > 1 row in set (0.00 sec) > > Which one is right? > > My opinion is that MariaDB's answer is definitely incorrect. > > As for MySQL's answer, it depends on how the result of JSONPath expression > is > defined. > > If it is "a set of nodes in the JSON document which match the pattern", > MySQL's > result is correct. > > Coming from XPath world, I was expecting a semantics in form > > find the set of nodes matching the search step#1 ( $**, > then apply step #2 ( .child1) > then apply step #3 ( any children of those) > ... > > in which case "124" would be in the result twice as it is reachable via two > possible paths. > > Any thoughts about this? > > BR > Sergei > -- > Sergei Petrunia, Software Developer > MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog > > >
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