Cast int string to JSON results in wrong type

[morgo]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

select CAST("9223372036854775808" as json);
select json_type(CAST("9223372036854775808" as json));

2. What did you expect to see? (Required)

mysql [localhost:8022] {msandbox} (test) > select CAST("9223372036854775808" as json);
+-------------------------------------+
| CAST("9223372036854775808" as json) |
+-------------------------------------+
| 9223372036854775808                 |
+-------------------------------------+
1 row in set (0.00 sec)

mysql [localhost:8022] {msandbox} (test) > select json_type(CAST("9223372036854775808" as json));
+------------------------------------------------+
| json_type(CAST("9223372036854775808" as json)) |
+------------------------------------------------+
| UNSIGNED INTEGER                               |
+------------------------------------------------+
1 row in set (0.00 sec)

3. What did you see instead (Required)

mysql> select CAST("9223372036854775808" as json);
+-------------------------------------+
| CAST("9223372036854775808" as json) |
+-------------------------------------+
| 9223372036854776000                 |
+-------------------------------------+
1 row in set (0.00 sec)

mysql> select json_type(CAST("9223372036854775808" as json));
+------------------------------------------------+
| json_type(CAST("9223372036854775808" as json)) |
+------------------------------------------------+
| DOUBLE                                         |
+------------------------------------------------+
1 row in set (0.00 sec)

4. What is your TiDB version? (Required)

mysql> SELECT tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v4.0.0-beta.2-1770-g51fbf415c
Edition: Community
Git Commit Hash: 51fbf415c904ad77b2a4c29fbfb3ff513ed60f8c
Git Branch: master
UTC Build Time: 2020-12-09 14:19:36
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)

[ti-srebot]

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