看看这个例子：
mysql> SELECT o_id, attribute, value FROM t3;
±-----±----------±------+
| o_id | attribute | value |
±-----±----------±------+
| 2 | color | red |
| 2 | fabric | silk |
| 3 | color | green |
| 3 | shape | square|
±-----±----------±------+
4 rows in set (0.00 sec)

mysql> SELECT o_id, JSON_OBJECTAGG(attribute, value)
> FROM t3 GROUP BY o_id;
±-----±--------------------------------------+
| o_id | JSON_OBJECTAGG(attribute, value) |
±-----±--------------------------------------+
| 2 | {“color”: “red”, “fabric”: “silk”} |
| 3 | {“color”: “green”, “shape”: “square”} |
±-----±--------------------------------------+
2 rows in set (0.00 sec)