The mode specifies whether the week starts on Sunday or Monday.
If the mode argument is omitted, the value of the default_week_format system variable is used.
The mode could be 0 ,1 ,2 ,3 ,4 ,5 ,6 ,7
mysql>
mysql> SELECT WEEK('1998-02-20');
+--------------------+
| WEEK('1998-02-20') |
+--------------------+
| 7 |
+--------------------+
1 row in set (0.00 sec)
mysql> SELECT WEEK('1998-02-20',0);
+----------------------+
| WEEK('1998-02-20',0) |
+----------------------+
| 7 |
+----------------------+
1 row in set (0.00 sec)
mysql> SELECT WEEK('1998-02-20',1);
+----------------------+
| WEEK('1998-02-20',1) |
+----------------------+
| 8 |
+----------------------+
1 row in set (0.00 sec)
mysql> SELECT WEEK('1998-12-31',1);
+----------------------+
| WEEK('1998-12-31',1) |
+----------------------+
| 53 |
+----------------------+
1 row in set (0.02 sec)
mysql> SELECT WEEK('2000-01-01',2);
+----------------------+
| WEEK('2000-01-01',2) |
+----------------------+
| 52 |
+----------------------+
1 row in set (0.00 sec)
mysql>