特殊数据类型表约束表连接索引触发器安全性DB设计

 alter table student modify id int primary key;主銉不可重复修改 alter table student modify id int auto_increment;

特殊数据类型EnumSetTextBlobTIMESTAMP 默认值create table users (    id integer,     name varchar(20),     likes enum (‘game‘,‘sleep‘,‘film‘));show  create table users；

MySQL约束常见约束检查约束(MySQL目前不支持)非空约束not null唯一约束unique主键约束外键约束定义唯一约束unique     unique(列1,列2)定义非空约束not null定义主键约束  primary key:不允许为空，不允许重复  删除主键：alter table tablename drop primary key ;定义主键自动增长  auto_increment主键一般的自动增长中在一起使用。定义外键约束constraint ordersid_FK foreign key(ordersid) references orders(id),删除外键约束alter table orders drop foreign key ordersid_FK;增加外键约束

索引作用索引支持索引分类索引创建索引设计Orcale索引

table_reference [INNER | CROSS] JOIN table_factor [join_condition]  | table_reference STRAIGHT_JOIN table_factor  | table_reference STRAIGHT_JOIN table_factor ON condition  | table_reference LEFT [OUTER] JOIN table_reference join_condition  | table_reference NATURAL [LEFT [OUTER]] JOIN table_factor  | table_reference RIGHT [OUTER] JOIN table_reference join_condition  | table_reference NATURAL [RIGHT [OUTER]] JOIN table_factor 

连接分类交叉连接内连接左外连接右外连接全连接自连接