Bigint unsigned column value in CASE WHEN operator is converted to bigint signed

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

drop table if exists t1;
create table t1(a int, b bigint unsigned);
insert into t1 (a, b) values (1,4572794622775114594), (2,18196094287899841997),(3,11120436154190595086);
select (case t1.a when 0 then 0 else t1.b end), cast(t1.b as signed)  from t1;

See also https://bugs.mysql.com/bug.php?id=79657
2. What did you expect to see?

mysql> select (case t1.a when 0 then 0 else t1.b end), cast(t1.b as signed)  from t1;
+-----------------------------------------+----------------------+
| (case t1.a when 0 then 0 else t1.b end) | cast(t1.b as signed) |
+-----------------------------------------+----------------------+
|                     4572794622775114594 |  4572794622775114594 |
|                    18196094287899841997 |  -250649785809709619 |
|                    11120436154190595086 | -7326307919518956530 |
+-----------------------------------------+----------------------+
3 rows in set (0.01 sec)

3. What did you see instead?

mysql> select (case t1.a when 0 then 0 else t1.b end), cast(t1.b as signed)  from t1;
+-----------------------------------------+----------------------+
| (case t1.a when 0 then 0 else t1.b end) | cast(t1.b as signed) |
+-----------------------------------------+----------------------+
|                     4572794622775114594 |  4572794622775114594 |
|                     -250649785809709619 |  -250649785809709619 |
|                    -7326307919518956530 | -7326307919518956530 |
+-----------------------------------------+----------------------+
3 rows in set (0.00 sec)

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

mysql> select tidb_version();
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                                                        |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v3.0.0-beta-260-g47a564b-dirty
Git Commit Hash: 47a564be2fc6045c6423e63b28a421924d5557bf
Git Branch: master
UTC Build Time: 2019-03-22 07:10:11
GoVersion: go version go1.12 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

[jackysp]

Thanks for your report, @wjhuang2016 !
I've reproduced it.
PTAL @XuHuaiyu

[ghost]

Confirming this issue still exists in master:

drop table if exists t1;
create table t1(a int, b bigint unsigned);
insert into t1 (a, b) values (1,4572794622775114594), (2,18196094287899841997),(3,11120436154190595086);
select (case t1.a when 0 then 0 else t1.b end), cast(t1.b as signed)  from t1;

..

mysql> select (case t1.a when 0 then 0 else t1.b end), cast(t1.b as signed)  from t1;
+-----------------------------------------+----------------------+
| (case t1.a when 0 then 0 else t1.b end) | cast(t1.b as signed) |
+-----------------------------------------+----------------------+
|                     4572794622775114594 |  4572794622775114594 |
|                     -250649785809709619 |  -250649785809709619 |
|                    -7326307919518956530 | -7326307919518956530 |
+-----------------------------------------+----------------------+
3 rows in set (0.00 sec)

mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v4.0.0-beta.2-750-g8a661044c
Edition: Community
Git Commit Hash: 8a661044cedf8daad1de4fbf79a390962b6f6c3b
Git Branch: master
UTC Build Time: 2020-07-10 10:52:37
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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