在Oralce中有个数据切割函数： substr。
substr('要切割的值',从第几个位置开始切割,切割几位);
如下例：
substr('hello word', 3, 2) would return 'll'
substr('hello word', 5) would return 'o word'
substr('hello word', -3, 3) would return 'ord'
substr('hello word', -6, 3) would return 'o w'
substr('hello word', -8, 2) would return 'll'