DB2无REGEX环境下处理Maximo导入CLOB中的HTML富文本

Got it, let's tackle this problem head-on—stripping HTML tags from Maximo-imported CLOB data when your DB2 environment doesn't support regex. Here are three practical, regex-free approaches you can use:

1. Nested REPLACE for Known, Limited Tag Sets #

If the HTML tags in your data are predictable (think common Maximo ones like <p>, <br>, <b>, <i>), you can chain REPLACE calls to strip them out. Just make sure to cast your CLOB to a compatible string type first (adjust the VARCHAR length based on your data size):

SELECT 
  REPLACE(
    REPLACE(
      REPLACE(
        REPLACE(
          CAST(your_clob_column AS VARCHAR(32672)), -- Tweak length to match your max data size
          '<p>', ''
        ),
        '</p>', ''
      ),
      '<br>', CHAR(10) -- Replace line break tags with actual newlines
    ),
    '</b>', ''
  ) AS cleaned_text
FROM your_table_name;

Heads up: If your CLOBs exceed the maximum VARCHAR length (varies by DB2 version, usually 32672 or 65535), use DBMS_LOB.SUBSTR to process chunks of the data. This method is quick but only scales well if you have a small, fixed set of tags.

2. Custom User-Defined Function (UDF) for Universal Tag Stripping #

For a more flexible solution that handles any HTML tag, create a recursive UDF that finds and removes all content between < and >:

CREATE OR REPLACE FUNCTION STRIP_HTML_TAGS(input CLOB)
RETURNS CLOB
LANGUAGE SQL
DETERMINISTIC
BEGIN
  DECLARE start_tag_pos INT;
  DECLARE end_tag_pos INT;
  DECLARE cleaned_clob CLOB;
  
  SET cleaned_clob = input;
  
  -- Locate the first opening tag
  SET start_tag_pos = LOCATE('<', cleaned_clob);
  WHILE start_tag_pos > 0 DO
    -- Find the matching closing > for the tag
    SET end_tag_pos = LOCATE('>', cleaned_clob, start_tag_pos);
    IF end_tag_pos > 0 THEN
      -- Remove the entire tag from < to >
      SET cleaned_clob = SUBSTR(cleaned_clob, 1, start_tag_pos - 1) || SUBSTR(cleaned_clob, end_tag_pos + 1);
    ELSE
      -- Exit loop if no closing > is found (unlikely with Maximo data)
      LEAVE;
    END IF;
    -- Look for the next tag
    SET start_tag_pos = LOCATE('<', cleaned_clob);
  END WHILE;
  
  RETURN cleaned_clob;
END;

Once the UDF is created, call it like this:

SELECT STRIP_HTML_TAGS(your_clob_column) AS cleaned_text FROM your_table_name;

This method works for any HTML tag (including self-closing ones like <img/>), though you might want to add extra logic if you need to preserve specific attributes or handle edge cases like escaped > characters (rare in Maximo exports).

3. XQuery for Well-Formed XHTML #

If your Maximo-exported HTML is actually valid XHTML (well-formed XML), you can use DB2's built-in XQuery support to extract pure text directly:

SELECT 
  XMLCAST(
    XMLQUERY('fn:data($doc/node())' PASSING XMLPARSE(DOCUMENT your_clob_column) AS "doc") 
    AS CLOB
  ) AS cleaned_text
FROM your_table_name;

Note: This will fail if your HTML isn't strictly valid (e.g., missing closing tags, unquoted attributes). Maximo sometimes exports well-formed XHTML, but test this with a sample first to avoid errors.

内容的提问来源于stack exchange，提问作者Shahvez Irfan