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

Running a quick test in MySQL 5.1 with a VARCHAR column set to latin1_bin I inserted some non-latin chars

INSERT INTO Test VALUES ('英國華僑');

I select them and get rubbish (as expected).

SELECT text from Test;

gives

text
????

I then changed the collation of the column to utf8_unicode and re-ran the SELECT and it shows the same result

text
????

This is what I would expect - It will keep the data and the data will remain rubbish, because when the data was inserted the column lost the extra character information and just inserted a ? for each non-latin character and there is no way for the ???? to again become 英國華僑.

Your data will stay in place but it won't be fixed.