substr函数怎么使用?

cjf107

最初由 tony110893 发布
[B].....................
The following example returns several specified substrings of "ABCDEFG":
SELECT SUBSTR(’ABCDEFG’,3,4) "Substring"
FROM DUAL;
Substring
---------
CDEF
SELECT SUBSTR(’ABCDEFG’,-5,4) "Substring"
FROM DUAL;
Substring
---------
CDEF
Assume a double-byte database character set:
SELECT SUBSTRB(’ABCDEFG’,5,4.2) "Substring with bytes"
FROM DUAL;
Substring with bytes
--------------------
CD [/B]

就如同3楼说的，最后一个例子:
10:09:10 SQL> SELECT SUBSTR('ABCDEFG',3,4) "Substring"
10:09:28   2  FROM DUAL;
CDEF

10:09:29 SQL> SELECT SUBSTR('ABCDEFG',-5,4) "Substring"
10:09:35   2  FROM DUAL;
CDEF

10:09:36 SQL> SELECT SUBSTRB('ABCDEFG',5,4.2) "Substring with bytes"
10:10:04   2  FROM DUAL;
EFG

susan_huangyong

最初由 wenxin2005 发布
[B]substri(str,length(str)-3, 3)
但是不太明白楼上说的最后一个例子，能说明一下吗，我也有这个参考手册。
为什么从5开始获取的子串会是CD？ [/B]