Oracle 选择当前日期前一周的数据

select * from sales_table where day_field between to_number(to_char(sysdate - 7, 'yyyymmdd')) and to_number(to_char(sysdate, 'yyyymmdd'))

其中，day_cd 形如 20181123，若day_cd 形如 2018-11-23，则为如下语句：

select * from sales_table where day_field between to_number(to_char(sysdate - 7, 'yyyy-mm-dd')) and to_number(to_char(sysdate, 'yyyy-mm-dd'))