WEEK(date[,mode])

此函數返回日期的周數。雙參數的形式WEEK()允許你指定星期是否開始於周日或周一，以及是否返回值應在範圍從0到53或從1到53。 如果省略了mode參數，係統default_week_format變量的值被使用

Mode	一個星期的第一天	範圍	Week 1 是第一個星期
0	Sunday	0-53	with a Sunday in this year
1	Monday	0-53	with more than 3 days this year
2	Sunday	1-53	with a Sunday in this year
3	Monday	1-53	with more than 3 days this year
4	Sunday	0-53	with more than 3 days this year
5	Monday	0-53	with a Monday in this year
6	Sunday	1-53	with more than 3 days this year
7	Monday	1-53	with a Monday in this year

mysql> SELECT WEEK('1998-02-20');
+---------------------------------------------------------+
| WEEK('1998-02-20')                                      |
+---------------------------------------------------------+
| 7                                                       |
+---------------------------------------------------------+
1 row in set (0.00 sec)