CREATE DATABASE db_name DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;

CREATE DATABASE 的语法：
CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name
[create_specification [, create_specification] ...]
create_specification:
[DEFAULT] CHARACTER SET charset_name
| [DEFAULT] COLLATE collation_name

更改数据库的字符编码
ALTER DATABASE db_name DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci