use my_database; -- preserve your old data in blob type
alter table my_tabe change my_column my_column blob; -- set your default encoding to utf8
alter table my_table convert to character set utf8; -- tell sql server your old code page ( i.e.: cp1256 )
alter table my_table change my_column my_column text charset {{code page}};
-- convert old text columns to blob,
ALTER TABLE my_table CHANGE my_column_name my_column_name BLOB; -- then update table character set
ALTER ignore TABLE my_table CONVERT TO CHARACTER SET utf8; -- then convert the text columns back to text type
ALTER TABLE my_table CHANGE my_column_name my_column_name TEXT;
-- If your old scripts break, try explicitly setting the names to UTF8 before making sql queries
SET NAMES utf8;
SELECT my_column_name FROM my_table limit 10;