Oracle正则表达式从最后一次出现时拆分字符串 [英] Oracle regular expression split string from last occurence

问题描述

我仍然在oracle中学习正则表达式，我陷入了中间，下面是我的示例代码:

I am still learning regexp in oracle I am stuck in middle, below is my sample code:

with t(val)
as
(
  --format: xyz_year_month_date
  select 'my_new_table_2015_06_31' from dual
  union all
  select 'my_new_table_temp_2016_06_31' from dual
 )
 select reverse(regexp_substr(reverse(val),'[^_]+',1,4)) col4,
 reverse(regexp_substr(reverse(val),'[^_]+',1,3)) col3,
 reverse(regexp_substr(reverse(val),'[^_]+',1,2)) col2,
 reverse(regexp_substr(reverse(val),'[^_]+',1,1)) col1
 from t;

Output:
COL4 COL3 COL2 COL1
table 2015 06 31
temp 2016 06 31

Expected output:
COL4 COL3 COL2 COL1
my_new_table 2015 06 31
my_new_table_temp 2016 06 31

谢谢.

推荐答案

您可以通过提取不同的捕获组(用圆括号()括起来)来实现无双重反转的操作:

You can do it without the double reverse by extracting different capture groups (surrounded in round () brackets):

WITH t ( VAL ) AS (
  SELECT 'my_new_table_2015_06_31' FROM DUAL UNION ALL
  SELECT 'my_new_table_temp_2016_06_31' FROM DUAL
)
SELECT REGEXP_SUBSTR( val, '^(.*)_([^_]+)_([^_]+)_([^_]+)$', 1, 1, NULL, 1 ) AS COL4,
       REGEXP_SUBSTR( val, '^(.*)_([^_]+)_([^_]+)_([^_]+)$', 1, 1, NULL, 2 ) AS COL3,
       REGEXP_SUBSTR( val, '^(.*)_([^_]+)_([^_]+)_([^_]+)$', 1, 1, NULL, 3 ) AS COL2,
       REGEXP_SUBSTR( val, '^(.*)_([^_]+)_([^_]+)_([^_]+)$', 1, 1, NULL, 4 ) AS COL1
FROM   t

您甚至可以通过使用以下命令使正则表达式简单得多:

You could even make the regular expression much simpler by just using:

'^(.+)_(.+)_(.+)_(.+)$'

第一个.+是贪婪的，因此它将尽可能匹配，直到第二到第四个捕获组中的最小匹配项所剩字符串不足为止.

The first .+ is greedy so it will match as much as possible until there is only enough of the string left for the minimum matches on the 2nd - 4th capturing groups.

但是，您不需要正则表达式:

WITH t ( VAL ) AS (
  SELECT 'my_new_table_2015_06_31' FROM DUAL UNION ALL
  SELECT 'my_new_table_temp_2016_06_31' FROM DUAL
)
SELECT SUBSTR( val, 1,        pos1 - 1        ) AS col4,
       SUBSTR( val, pos1 + 1, pos2 - pos1 - 1 ) AS col3,
       SUBSTR( val, pos2 + 1, pos3 - pos2 - 1 ) AS col2,
       SUBSTR( val, pos3 + 1                  ) AS col1
FROM   (
  SELECT val,
         INSTR( val, '_', -1, 1 ) AS pos3,
         INSTR( val, '_', -1, 2 ) AS pos2,
         INSTR( val, '_', -1, 3 ) AS pos1
  FROM   t
);

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