Bug #103690 Can't use ->> with an expression for the path

• Submitted: 13 May 2021 23:30
• Modified: 14 May 2021 11:50
• Reporter: Justin Levene
• Status: Duplicate
• Category: MySQL Server: JSON
• Severity: S4 (Feature request)
• Version: 8.0.23, 8.0.25
• OS: Any
• CPU Architecture: Any

[13 May 2021 23:30] Justin Levene

Description:
when using json->>"$.a" is fine,however using json->>concat("$.", "a") does not work

How to repeat:
select json_value('{"a":1, "b":2, "c":3}', "$.b"); is fine

The following do not work:

select json_value('{"a":1, "b":2, "c":3}', concat("$.","b") );

or

set @path = "$.b";
select json_value('{"a":1, "b":2, "c":3}', @path);

Suggested fix:
Allow expressions and variables in the path

[13 May 2021 23:32] Justin Levene

Also you can't use json->>concat("$.", "a")

[14 May 2021 6:36] MySQL Verification Team

Hello Justin Levene,

Thank you for the report and feedback.

regards,
Umesh

[14 May 2021 11:29] Knut Anders Hatlen

Thanks for the bug report.

WL#9124, which added the ->> syntax, mentions that only a string literal is accepted for the path. It doesn't mention why only string literals are accepted, but I seem to recall it would require some bigger changes in the parser to support more complex expressions, so only the limited syntax was implemented.

WL#12228, which added JSON_VALUE, also says the path has to be a string literal. In this case, the SQL standard specifies that <JSON path specification> ::= <character string literal>, so allowing expressions would be an extension to the standard syntax.

Since this is a request for implementing more syntax, I'm reclassifying it from bug to feature request.

[14 May 2021 11:50] Knut Anders Hatlen

Closing as a duplicate of bug#87360.