unix_timestamp is not compatible with Mysql

[qw4990]

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.

select @a:=FROM_UNIXTIME(1);
select unix_timestamp(@a);

2. What did you expect to see?
   In Mysql

mysql> select @a:=FROM_UNIXTIME(1);
+----------------------+
| @a:=FROM_UNIXTIME(1) |
+----------------------+
| 1970-01-01 08:00:01  |
+----------------------+
1 row in set (0.00 sec)

mysql> select unix_timestamp(@a);
+--------------------+
| unix_timestamp(@a) |
+--------------------+
|                  1 |
+--------------------+
1 row in set (0.00 sec)

3. What did you see instead?
   In TiDB

mysql> select @a:=FROM_UNIXTIME(1);
+----------------------+
| @a:=FROM_UNIXTIME(1) |
+----------------------+
| 1970-01-01 08:00:01  |
+----------------------+
1 row in set (0.00 sec)

mysql> select unix_timestamp(@a);
+--------------------+
| unix_timestamp(@a) |
+--------------------+
|           1.000000 |
+--------------------+
1 row in set (0.01 sec)

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

+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                                                     |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v3.0.0-beta-212-g0681b8125
Git Commit Hash: 0681b8125080045ee0d4747ce61923164c6f2dd1
Git Branch: master
UTC Build Time: 2019-03-14 04:39:19
GoVersion: go version go1.12 darwin/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

[qw4990]

As discussion in #9751, #10168, #9861, this issue can't be fixed now.