Indexing mariadb中键列中的Mul值
我已经在mariadb中创建了dept表,dno作为主键。然后我创建了emp表,eno作为主键,dno作为外键,如下所示:Indexing mariadb中键列中的Mul值,indexing,key,mariadb,Indexing,Key,Mariadb,我已经在mariadb中创建了dept表,dno作为主键。然后我创建了emp表,eno作为主键,dno作为外键,如下所示: create table dept(dno int primary key,dname varchar(20)); create table emp(eno int primary key,ename varchar(20),dno int,foreign key(dno) references dept(dno)); 然后我描述两个表 DESC emp; +------
create table dept(dno int primary key,dname varchar(20));
create table emp(eno int primary key,ename varchar(20),dno int,foreign key(dno) references dept(dno));
然后我描述两个表
DESC emp;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| eno | int(11) | NO | PRI | NULL | |
| ename | varchar(20) | YES | | NULL | |
| dno | int(11) | YES | MUL | NULL | |
+-------+-------------+------+-----+---------+-------+
desc dept;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| dno | int(11) | NO | PRI | NULL | |
| dname | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
从emp表中删除外键dno后,它在emp表中显示相同的内容
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| eno | int(11) | NO | PRI | NULL | |
| ename | varchar(20) | YES | | NULL | |
| dno | int(11) | YES | MUL | NULL | |
+-------+-------------+------+-----+---------+-------+
如果删除外键约束,如何删除多值键列请使用正确的格式。这是无法访问的请使用
显示创建表
;它比描述
更具描述性。(它将部分回答您的问题。)