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

It's simpler

UPDATE table_name SET column_name = CONCAT('A',SUBSTRING(column_name, INSTR(column_name, 'B') + LENGTH('A')));