MySQL JSON_OBJECT() with some fields already containing JSON String

问题

How to get a JSON_OBJECT() of 3 columns whose some contains already a JSON format string.

Here is my example with info field that contains a json string, so all this object is escaped :

SELECT 
    T1.id, 
    CONCAT(
        '{"elements": [',
        GROUP_CONCAT(
            JSON_OBJECT(
                'type',  T2.`type`,
                'data',  T2.`data`,
                'info',  T2.`info`  <<-- JSON stored string in varchar(100)
            )
        ),
        ']}'
    ) AS `elements`,
FROM `table` T1
INNER JOIN `table2` T2
    ON T1.`id` = T2.`fk_t1_id`
GROUP BY T1.`id`

Maybe, use the new storage functions for JSON format will be better, but I didn't test it yet. What do you think ?

回答1:

Best solution I found is to use JSON_MERGE() in combination with JSON_OBJECT() and CONCAT()

SELECT 
    T1.id, 
    CONCAT(
        '{"elements": [',
        GROUP_CONCAT(
            JSON_MERGE(
                JSON_OBJECT(
                    'type',  T2.`type`,
                    'data',  T2.`data`
                ),
                CONCAT('{"info": ',  T2.`info`, '}')
            )
        ),
        ']}'
    ) AS `elements`,
FROM `table` T1
INNER JOIN `table2` T2
    ON T1.`id` = T2.`fk_t1_id`
GROUP BY T1.`id`

来源：https://stackoverflow.com/questions/45278721/mysql-json-object-with-some-fields-already-containing-json-string