MySQL的存储引擎（二）解决Warning Code : 3719 'utf8' is currently an alias for the character set UTF8MB3,...

1.外键约束：MySQL支持外键的常用存储引擎只有InnoDB，在创建外键的时候，要求父表必须有对应的索引，子表在创建外键的时候也会自动创建对应的索引。

CREATE TABLE country(
    country_id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
    country VARCHAR(50) NOT NULL,
    last_update TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    PRIMARY KEY (country_id)
) ENGINE=INNODB DEFAULT CHARSET=utf8;

CREATE TABLE city (
    city_id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
    city VARCHAR(50) NOT NULL,
    country_id SMALLINT UNSIGNED NOT NULL,
    last_update TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    PRIMARY KEY (city_id),
    KEY idx_fk_country_id (country_id),
    CONSTRAINT fk_city_country FOREIGN KEY (country_id) REFERENCES country (country_id) ON DELETE RESTRICT ON UPDATE CASCADE 
) ENGINE=INNODB DEFAULT CHARSET=utf8;

 1 warnings：

Warning Code : 3719 'utf8' is currently an alias for the character set UTF8MB3, but will be an alias for UTF8MB4 in a future release. Please consider using UTF8MB4 in order to be unambiguous.

查看下mysql字符集

 SHOW VARIABLES WHERE Variable_name LIKE 'character\_set\_%' OR Variable_name LIKE 'collation%';

修改默认字符集例句：
CREATE DATABASE IF NOT EXISTS database_name DEFAULT CHARSET utf8mb4 COLLATE utf8mb4_0900_ai_ci

CREATE TABLE city1 (
    city_id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
    city VARCHAR(50) NOT NULL,
    country_id SMALLINT UNSIGNED NOT NULL,
    last_update TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    PRIMARY KEY (city_id),
    KEY idx_fk_country_id (country_id),
    CONSTRAINT fk_city_country FOREIGN KEY (country_id) REFERENCES country (country_id) ON DELETE RESTRICT ON UPDATE CASCADE 
) ENGINE=INNODB DEFAULT CHARSET utf8mb4 COLLATE utf8mb4_0900_ai_ci

不再报错：