-- 查看当前数据库支持的存储引擎
SHOW ENGINES;
-- VALUE为disable的记录表示支持该引擎，但是数据库启动时被禁用
show VARIABLES LIKE 'have%';

create table autoincre_demo(i SMALLINT NOT NULL auto_increment,NAME VARCHAR(10),PRIMARY KEY(i)
)ENGINE=INNODB;
INSERT INTO autoincre_demo VALUES(1,'1'),(0,'2'),(NULL,'3');
SELECT * FROM autoincre_demo;                                                                                                           

use test01;
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(5) unsigned NOT NULL auto_increment,`city` varchar(50) NOT NULL,`country_id` smallint(5) 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;insert into country(country_id, country) values(1, "china");
insert into city(city_id, city, country_id) values(200, "wenzhou", 1); SELECT * from country WHERE country_id = 1;
SELECT * from city WHERE country_id =1;
-- 执行删除语句报错。不能删除
DELETE FROM country where country_id=1;
-- 可以update,执行这条语句时，字表city的country_id字段也被修改。
-- CASCADE 表示父表在更新或者删除时，子表对应记录也被更新或者删除
-- set null 表示如果父表进行更新或删除操作，子表对应字段被set NULL
-- RESTRICT 和no action 相同，限制子表有关联记录情况下父表不能更新
update country set country_id =1 WHERE country_id =1000;