如何在sql中提取周数

Question

我有一个varchar2类型的transdate列,它有以下主菜

01/02/2012
01/03/2012

等等

我使用to_date函数将其转换为另一列中的日期格式.这是我得到的格式.

01-JAN-2012
03-APR-2012

当我试图提取weekno时,我得到所有空值.

选择to_char(to_date(TRANSDATE),'w')作为tablename的weekno.

null
null

如何以上述格式从日期获取weekno？

Answer 1

将varchar2日期转换为true date数据类型后,转换回varchar2所需的掩码:

to_char(to_date('01/02/2012','MM/DD/YYYY'),'WW')

如果您想要number数据类型中的周数,可以将语句包装在to_number():

to_number(to_char(to_date('01/02/2012','MM/DD/YYYY'),'WW'))

但是,您需要考虑几周的数字选项:

WW  Week of year (1-53) where week 1 starts on the first day of the year and continues to the seventh day of the year.
W   Week of month (1-5) where week 1 starts on the first day of the month and ends on the seventh.
IW  Week of year (1-52 or 1-53) based on the ISO standard.

Answer 2

尝试将 'w' 替换为 'iw'。例如：

SELECT to_char(to_date(TRANSDATE, 'dd-mm-yyyy'), 'iw') as weeknumber from YOUR_TABLE;