oracle sql中的regexp_substr

Question

我碰壁了。我需要从下面的文本中提取 from: Date 和 To: Date。 它总是以日期开头。但是从：更改为：有时可以是 [none] 而不是日期模式。

列：

"31-Jul-2017 11:29 (GMT+1:00) Date Due was modified by: placeholder, SNO-1234.

**Changed from: 12-Dec-2017**

**Changed to: 01-Jan-2021**

Meaning: Initial Entry 
Meaning Comments:"

想要的输出：

Column = From: "12-Dec-2017"       
Column = Changed To: "01-Jan-2021"

我试过了

cast(regexp_substr(column:, 'from:\s.*') as varchar(17)) as "From:",

cast(regexp_substr(column:, 'to:\s.*') as varchar(15)) as "Changed To:"

我最终得到..

Column = From: "**From:** 12-Dec-2017"                     
Column = Changed To: "**To:** 01-Jan-2021"
   

无论如何要排除 from: 和 to: ？所以基本上，我怎样才能只得到“from：”和“to：”之后的 11 个字符。

提前致谢！

\光辉之水

Answer 1

你不需要正则表达式，你可以使用简单的字符串函数：

SELECT CASE 
       WHEN from_pos > 0
       THEN TO_DATE(
              SUBSTR( value, from_pos + 14, 11 )
              DEFAULT NULL ON CONVERSION ERROR,
              'DD-MON-YYYY'
            )
       END AS from_dt,
       CASE
       WHEN to_pos > 0
       THEN TO_DATE(
              SUBSTR( value, to_pos + 12, 11 )
              DEFAULT NULL ON CONVERSION ERROR,
              'DD-MON-YYYY'
            )
       END AS to_dt
FROM   (
  SELECT value,
         INSTR( LOWER( value ), 'changed from: ', 1, 1 ) AS from_pos,
         INSTR( LOWER( value ), 'changed to: ', 1, 1 ) AS to_pos
  FROM   table_name
);

但是，如果您确实想使用（较慢的）正则表达式，那么您可以使用：

SELECT TO_DATE(
         REGEXP_SUBSTR(
           value,
           'changed from:\s*(([012]\d|3[01])-(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)-\d{4})',
           1,
           1,
           'i',
           1
         )
         DEFAULT NULL ON CONVERSION ERROR,
         'DD-MON-YYYY'
       ) AS from_dt,
       TO_DATE(
         REGEXP_SUBSTR(
           value,
           'changed to:\s*(([012]\d|3[01])-(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)-\d{4})',
           1,
           1,
           'i',
           1
         )
         DEFAULT NULL ON CONVERSION ERROR,
         'DD-MON-YYYY'
       ) AS to_dt
FROM   table_name;

其中，对于您的示例数据：

CREATE TABLE table_name ( value ) AS
SELECT '31-Jul-2017 11:29 (GMT+1:00) Date Due was modified by: placeholder, SNO-1234.
Changed from: 12-Dec-2017
Changed to: 01-Jan-2021
Meaning: Initial Entry Meaning Comments:' FROM DUAL

两个输出：

FROM_DT | TO_DT :----------------- | :----------------- 2017-12-12T00:00:00 | 2021-01-01T00:00:00

db小提琴here