What will happen to existing data if I change the collation of a column in MySQL?

Question

I am running a production application with MySQL database server. I forget to set column\'s collation from latin to utf8_unicode, which results in

Answer 1

CAUTION! Some problems are solved via

ALTER TABLE ... CONVERT TO ...

Some are solved via a 2-step process

ALTER TABLE ... MODIFY ... VARBINARY...
ALTER TABLE ... MODIFY ... VARCHAR...

If you do the wrong one, you will have a worse mess!

1. Do SELECT HEX(col), col ... to see what you really have.
2. Study this to see what case you have: Trouble with utf8 characters; what I see is not what I stored
3. Perform the correct fix, based on these cases: http://mysql.rjweb.org/doc.php/charcoll#fixes_for_various_cases