时间类转字符、时间天数计算

<p>select * from g_inouttblbill where hdlflag='1' and iodate > to_char (date '2015-10-26' - integer '7', 'YYYYmmdd') and iodate < to_char (date '2015-10-26' + integer '7', 'YYYYmmdd') and ioflag =3 and iotype=1</p>