在MySQL中,使用外键需要满足以下条件: 在创建表时,需要在字段定义中使用FOREIGN KEY关键字指定外键; 外键字段的数据类型必须与被引用字段的数据类型一致; 外键字段必须创建索引。 以下是使用外键的语法示例: CREATETABLE表名(列1数据类型,列2数据类型,...FOREIGNKEY(外键字段)REFERENCES被引用表名(被引用字段)); 1....
For example, you cannot create an order for a non-existent customer. In addition, you can set up a cascade on delete action for the customerNumber foreign key so that when you delete a customer in the customers table, all the orders associated with the customer are also deleted. This ...
SET FOREIGN_KEY_CHECKS = 1; As mentioned, this is a bit of an obscure technique, combining this MySQL foreign keys check with the need to drop a database table and then re-create the table, while the table had very little data in it, but hey, if it helps anyone else, I'm happy ...
mysql> create table tb_employee1(id int(11)primary key,name varchar(25),depld int(11),salary float); mysql> create table tb_employee1(id int(11),name varchar(25),depld int(11),salary float,primary key(id)); 1. 2. (2)多字段联合主键 mysql> create table tb_employee1(id int(11)...
create table course ( cno int primary key, cname char(255), cpno int, ccredit int, foreign key(cpno)references course(cno) ); insert into course(cno,cname,cpno,ccredit) values (2,'数学',null,2); insert into course(cno,cname,cpno,ccredit) ...
show create table +数据表名字; 4.增改 alter table 表名 add/change 5.删除 drop table +数据表名字; 6.给表重新命名 alter table 表名 rename to 新表名; 三.DML数据元素操作 操作方法 因为这是表中数据处理,不用额外加table,而是直接加表名就行 ...
foreign key(addrid) references test1(id)); 表2: create table test1( id int not null primary key, name varchar(20) ); 查看表结构: SELECT TABLEDEF(‘SYSDBA’,’TEST’); 2、create table as方式建表与test相同表结构。 创建表: Create table test1as as select * from test1; ...
The table name can be specified as db_name.tbl_name to create the table in a specific database. This works regardless of whether there is a default database, assuming that the database exists. If you use quoted identifiers, quote the database and table names separately. For example, write...
SET@OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS; 2 SETFOREIGN_KEY_CHECKS=0; 3 SOURCE/backups/mydump.sql;-- restore your backup within THIS session 4 SETFOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS; Example: 27 1 mysql>CREATETABLEchild ( ...
创建数据库 Create database db_name[数据库选项]; 显示所有数据库 show databases; 查看数据库创建语句 show create batabase db_name; 数据库删除 drop database db_name; 修改数据库 alter database db_name 指令; 表操作 创建表 create table 库名.tbl_name(列结构)[表选项]; 列定义:列名 数据类型[列...