在做系统时,经常会遇到在一个字段中,用逗号或其他符号分隔存储多个信息,例如保存某个用户的一对多权限时,在权限组这个字段中,就会逗号分隔保存多个权限编号。
那么,现在如果给出一个权限编号,要去检索出用后这个权限的用户集合,就会需要在逗号分隔的多个权限编号中去匹配给出的这个权限编号。如果使用like去做,一则效率不高,二则匹配不精确。因此用到了逗号分隔列转行的方法。目前该方法只适合在oracle数据库中使用。该方法只需要sql语句就可以实现列转行。下面给出该方法的示例:
select a,b,c from
(with test as (select 'aaa' a,'bbb' b,'1,2,3' c from dual)
select a,b,substr(t.ca,instr(t.ca, ',', 1, c.lv) + 1,instr(t.ca, ',', 1, c.lv + 1) - (instr(t.ca, ',', 1, c.lv) + 1)) AS c
from (select a,b,',' || c || ',' AS ca,length(c || ',') - nvl(length(REPLACE(c, ',')), 0) AS cnt FROM test) t,
(select LEVEL lv from dual CONNECT BY LEVEL
执行以上代码,结果如下图:
模拟数据列 c 中的内容“1,2,3”被转成了三行,前面两列的内容同时附带过去。在实际运用时,只要把
select 'aaa' a,'bbb' b,'1,2,3' c from dual 替换成实际需要转换的数据表中的字段即可,其中c字段必须是要进行转换的保存逗号分隔内容的字段。下面的内容都可以不需要更改。其中“LEVEL

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