SQL: search/replace but only the first time a value appears in record

Question

I have html content in the post_content column.

I want to search and replace A with B but only the first time A appears in the record as it may appear more than onc

Answer 1

With reference to https://dba.stackexchange.com/a/43919/200937 here is another solution:

UPDATE wp_posts 
SET post_content = CONCAT( LEFT(post_content , INSTR(post_content , 'A') -1),
                           'B',
                           SUBSTRING(post_content, INSTR(post_content , 'A') +1))
WHERE INSTR(post_content , 'A') > 0;

If you have another string, e.g. testing then you need to change the +1 above to the according string length. We can use LENGTH() for this purpose. By the way, leave the -1 untouched.

Example: Replace "testing" with "whatever":

UPDATE wp_posts 
SET post_content = CONCAT( LEFT(post_content , INSTR(post_content , 'testing') -1),
                           'whatever',
                           SUBSTRING(post_content, INSTR(post_content , 'testing') + LENGTH("testing"))
WHERE INSTR(post_content , 'testing') > 0;

By the way, helpful to see how many rows will be effected:

SELECT COUNT(*)
FROM post_content 
WHERE INSTR(post_content, 'A') > 0;