REGEXP_SUBSTR函数，感觉像行专列

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/*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 DUALCONNECT BY LEVEL <= 7;--优化SELECT REGEXP_SUBSTR('17,20,23', '[^,]+', 1, LEVEL, 'i') AS STR FROM DUALCONNECT BY LEVEL <= LENGTH('17,20,23') - LENGTH(REGEXP_REPLACE('17,20,23', ',', '')) + 1;

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