Variable default_week_format doesn't work

[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.

mysql> set default_week_format = 6;
mysql> select week(20001231), week(20001231,6);

2. What did you expect to see?
   In Mysql

mysql>  set default_week_format = 6;
Query OK, 0 rows affected (0.00 sec)

mysql> select week(20001231), week(20001231,6);
+----------------+------------------+
| week(20001231) | week(20001231,6) |
+----------------+------------------+
|              1 |                1 |
+----------------+------------------+
1 row in set (0.00 sec)

3. What did you see instead?
   In TiDB

mysql> set default_week_format = 6;
Query OK, 0 rows affected (0.00 sec)

mysql> select week(20001231), week(20001231,6);
+----------------+------------------+
| week(20001231) | week(20001231,6) |
+----------------+------------------+
|             53 |                1 |
+----------------+------------------+
1 row in set (0.00 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-197-g52c8267a7
Git Commit Hash: 52c8267a735dbb5e14b07c361ab8caa3efff5631
Git Branch: master
UTC Build Time: 2019-03-12 06:53:10
GoVersion: go version go1.12 darwin/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)