[jira] [Commented] (CALCITE-2791) Add the JSON_TYPE function

["Hongze Zhang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-2791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16753160#comment-16753160 ] 

Hongze Zhang commented on CALCITE-2791:
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Sorry for the reassignation [~julianhyde], I am not sure why the assignee has been changed once I click the comment control.

Hi [~x1q1j1], I am not so familiar with the function JSON_TYPE (and also JSON_LENGTH suggested by the CALCITE-2810), anyway I know a little bit with the JSON function in Calcite or SQL standard, so maybe I can help provide some thoughts here.

1. I found some spec definitions from MySQL documentation about the function [JSON_TYPE|https://dev.mysql.com/doc/refman/8.0/en/json-attribute-functions.html#function_json-type] (and [JSON_LENGTH|https://dev.mysql.com/doc/refman/8.0/en/json-attribute-functions.html#function_json-length]). If the functions are not currently introduced by SQL standard and other SQL implementations, is it worth a discussion about whether to put them to SqlStdOperatorTable directly? (I personally have no objections – they are MySQL dialect function, but Calcite does not have a built-in MySQL function table so far, and there are already some MySQL dialect functions in SqlStdOperatorTable (e.g. the function TIMESTAMPADD)).

2. MySQL's [JSON_TYPE|https://dev.mysql.com/doc/refman/8.0/en/json-attribute-functions.html#function_json-type] function accepts only a single parameter, but I guess you intend to make it accept multiple (see [https://github.com/apache/calcite/pull/1013/files#diff-3969d844f7ecd2b3d324bf8b0e5a1e9aR5259]), what happens if more than one parameter are passed into the function?

3. MySQL's [JSON_TYPE|https://dev.mysql.com/doc/refman/8.0/en/json-attribute-functions.html#function_json-type] function categorizes numeric JSON values with there types: INTEGER, DOUBLE, and DECIMAL, I see you intend to categorize with INTEGER, LONG, DOUBLE, FLOAT. Does the types benefit users than just keeping up with MySQL?

> Add the JSON_TYPE function
> --------------------------
>
>                 Key: CALCITE-2791
>                 URL: https://issues.apache.org/jira/browse/CALCITE-2791
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>            Reporter: xuqianjin
>            Assignee: Julian Hyde
>            Priority: Major
>              Labels: https://github.com/apache/calcite/pull/1013
>
> The data in json can be =, <, <=, >, >=, <>,! =, and <=>. But the data types in json can be diverse, so when you compare different types, you have a priority, and the high priority is greater than the low priority (you can view the types with the JSON_TYPE() function). The priorities are as follows:
>  BOOLEAN
>  ARRAY
>  OBJECT
>  STRING
>  INTEGER
> LONG
> DOUBLE
>  NULL



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