Convert from json opaque value to other types are not supported

[YangKeao]

Enhancement

The following SQL will have different behavior for TiDB and MySQL:

select cast(cast(b'1011' as JSON) as UNSIGNED);

TiDB:

ERROR 1105 (HY000): Unknown type code in JSON

MySQL:

mysql> select cast(cast(X'01AF' as JSON) as SIGNED);
+---------------------------------------+
| cast(cast(X'01AF' as JSON) as SIGNED) |
+---------------------------------------+
|                                     0 |
+---------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+--------------------------------------------------------------------------+
| Level   | Code | Message                                                                  |
+---------+------+--------------------------------------------------------------------------+
| Warning | 3156 | Invalid JSON value for CAST to INTEGER from column cast_as_json at row 1 |
+---------+------+--------------------------------------------------------------------------+
1 row in set (0.00 sec)

[YangKeao]

Fixed, as we added opaque value support.