从日期字符串中提取日期编号

Question

是否可以从日期名称中提取整数值,即"Mon","Tue","Wed"和SQL语句？

例如:

 Mon = 1
 Tue = 2
 Wed = 3

Answer 1

尝试FIELD:

SELECT FIELD('Mon', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun');
    -> 1
SELECT FIELD('Thu', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun');
    -> 4

http://dev.mysql.com/doc/refman/5.4/en/string-functions.html#function_field

Answer 2

如果你只是有一个只有 Mon、Tue、Wed 等的非日期时间字段，你可以使用STR_TO_DATE()和WEEKDAY()函数来想出这样的东西：

SELECT WEEKDAY(STR_TO_DATE(CONCAT('201011 ', yourField), '%X%V %W')) + 1 AS WeekIndex;

测试用例：

SELECT WEEKDAY(STR_TO_DATE(CONCAT('201011 ', 'Mon'), '%X%V %W')) + 1 AS WeekIndex;
+-----------+
| WeekIndex |
+-----------+
|         1 |
+-----------+

SELECT WEEKDAY(STR_TO_DATE(CONCAT('201011 ', 'Tue'), '%X%V %W')) + 1 AS WeekIndex;
+-----------+
| WeekIndex |
+-----------+
|         2 |
+-----------+

SELECT WEEKDAY(STR_TO_DATE(CONCAT('201011 ', 'Wed'), '%X%V %W')) + 1 AS WeekIndex;
+-----------+
| WeekIndex |
+-----------+
|         3 |
+-----------+

SELECT WEEKDAY(STR_TO_DATE(CONCAT('201011 ', 'Thu'), '%X%V %W')) + 1 AS WeekIndex;
+-----------+
| WeekIndex |
+-----------+
|         4 |
+-----------+