How to change the default collation of a database ?

change database collation:

ALTER DATABASE <database_name> CHARACTER SET utf8 COLLATE utf8_general_ci;

change table collation:

ALTER TABLE <table_name> CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;


change column collation:

ALTER TABLE <table_name> MODIFY <column_name> VARCHAR(255) CHARACTER SET utf8 COLLATE utf8_general_ci;