SQL query to replace string based on wildcardt

问题:

I would like to run this type of query on my WP database to remove all span instances with id="more-":

UPDATE wp_posts SET post_content = REPLACE (
post_content,
'<p><span id="more-35075"></span></p>',
'');

But the number that follows the 'more-' in my example is a variable. How to write this query with someting like a wildcard: span id="more-*.

Thank you

回答1:

In MySQL version 8.0 and above, you can use REGEX_REPLACE() function. In absence of the same, some complicated string operations can be done. This is based on your confirmation, that the said sub-string is occurring only once in a value.

REPLACE() does not have any support for wildcards, patterns, regular expressions etc. It only replaces a given fixed substring with another fixed substring, in a bigger string.

Instead, we can try to extract portions of the post_content. We will extract the leading substring before the '<p><span id="more-' using Substring_Index() function. Similarly, we will extract the trailing substring after the '"></span></p>' portion.

Now, we can simply Concat() these portions to get the required post_content. You can find details of various String functions used here: https://dev.mysql.com/doc/refman/8.0/en/string-functions.html

I have also added a WHERE condition, so that we pick only those rows which match our given substring criteria.

UPDATE wp_posts 
SET post_content = 
CONCAT( 
       SUBSTRING_INDEX(post_content, 
                       '<p><span id="more-', 
                       1), 
       SUBSTRING(post_content, 
                 LOCATE('"></span></p>', 
                        post_content, 
                        LOCATE('<p><span id="more-',
                               post_content)
                        ) + 13) -- 13 is character length of "></span></p>
      )
WHERE post_content LIKE '%<p><span id="more-%"></span></p>%';

---

Query #1: Data before Update operations

SELECT * FROM wp_posts;

| post_content                                            |
| ------------------------------------------------------- |
| adasdaadsa<p><span id="more-35075"></span></p>121324124 |
| 1412123123<p><span id="more-232"></span></p>adasdaafas  |

---

Query #2: Data after Update operations

SELECT * FROM wp_posts;

| post_content         |
| -------------------- |
| adasdaadsa121324124  |
| 1412123123adasdaafas |

View on DB Fiddle