We are upgrading our server and I have this stored procedure that MySQL 8 really seems to hate. In real world usage I was seeing a complex select with multiple calls to it and 14K rows take 4 seconds on 5.6 and 20 minutes on MySQL 8. But I made it into a simple test case:
select like_alphanum_criteria('testval') from mytable;
MySQL 5.6: 478 rows in set (0.04 sec)
MySQL 8: 478 rows in set (8.26 sec)
This really becomes an issue with bigger tables. The stored procedure has no database interaction in it, so it's not an index or explain thing.
