Question

如何在知道当天的一个月内获得前一个星期。

例如，如果我有这样的表：

emp_num   trans_date 
  22       1-10-2015
  22       5-10-2015
  22       7-10-2015
  22       11-10-2015
  22       14-10-2015
  22       19-10-2015
  22       27-10-2015

现在每个月都有4个星期。

所以我的约会时间为11-10-2015（第二周）我希望在同一个月内获得前几周的结果。所以在这个例子中我想要10月份第一周的结果如下：

emp_num   trans_date 
  22       1-10-2015
  22       5-10-2015
  22       7-10-2015

注意：

The start day of the week is: sat

The end day of the week is:Fri

Answer 1

如果我理解您的问题，2015年10月，您会预料到以下结果：

RunDate     Weekday  Result
01-10-2015  Thurs    [nothing]
02-10-2015  Fri      [nothing]
03-10-2015  Sat      01-10-2015, 02-10-2015
04-10-2015  Sun      01-10-2015, 02-10-2015 (same as above)
...
09-10-2015  Fri      01-10-2015, 02-10-2015 (same as above)
10-10-2015  Sat      01-10-2015, ... , 09-10-2015
...
16-10-2015  Fri      01-10-2015, ... , 09-10-2015 (same as above)
17-10-2015  Sat      01-10-2015, ... , 16-10-2015
20-10-2015  Tue      01-10-2015, ... , 16-10-2015 (same as above)
30-10-2015  Fri      01-10-2015, ... , 23-10-2015
31-10-2015  Sat      01-10-2015, ... , 30-10-2015

如果是这种情况，则以下查询将执行您所需的操作：

SELECT trans_date, emp_num, COUNT(1)
  FROM transaction_table
  WHERE MONTH(trans_date) = MONTH(TODAY)
    AND YEAR(trans_date) = YEAR(TODAY)
    AND trans_date <= DECODE(WEEKDAY(TODAY),
                                6, TODAY -1,
                                TODAY - WEEKDAY(TODAY) -2)
GROUP BY 1, 2
ORDER BY 1, 2

DECODE()中的逻辑是管理WEEKDAY()默认行为的偏移量，其中Sun =＆gt; 0和Sat =＆gt; 6.上述查询中的关键字TODAY可以替换为变量或任意单个日期。

Answer 2

我还没有在informix中工作，但这是SQL中的样子：

DECLARE @SomeDate DATE
SET @SomeDate = '2015-10-11'  

DECLARE @DayOfWeek INT
SELECT @DayOfWeek = ((DATEPART(dw, @SomeDate) ) % 7)

DECLARE @WeekStart DATE
SELECT @WeekStart = DATEADD(d, -@DayOfWeek, @SomeDate)

SELECT * FROM SomeTable 
WHERE MONTH(trans_date) = MONTH(@SomeDate) AND trans_date < @WeekStart

如何获取同一个月前几周的数据，知道作为搜索点的那一天

2 个答案: