/*
REGEXP_SUBSTR函数格式如下:
function REGEXP_SUBSTR(String, pattern, position, occurrence, modifier)
__srcstr :需要进行正则处理的字符串
__pattern :进行匹配的正则表达式
__position :起始位置,从第几个字符开始正则表达式匹配(默认为1)
__occurrence :标识第几个匹配组,默认为1
__modifier :模式('i'不区分大小写进行检索;'c'区分大小写进行检索。默认为'c'。)
*/
--分割非逗号成组
--同样的功能
SELECT LEVEL FROM DUAL CONNECT BY LEVEL <= 7;
SELECT ROWNUM FROM DUAL CONNECT BY ROWNUM <= 7;
--原始
SELECT NVL(REGEXP_SUBSTR('17,20,23', '[^,]+', 1, LEVEL, 'i'), 'NULLL') AS STR
FROM DUAL
CONNECT BY LEVEL <= 7;
--优化
SELECT REGEXP_SUBSTR('17,20,23', '[^,]+', 1, LEVEL, 'i') AS STR
FROM DUAL
CONNECT BY LEVEL <= LENGTH('17,20,23') - LENGTH(REGEXP_REPLACE('17,20,23', ',', '')) + 1;
![](https://img-blog.csdn.net/20170222113953626?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvbHVtYW4xOTkx/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center)