百度试题 结果1 题目在SQL中,___约束旳关键字为primary key,___约束旳关键字为foreign key。相关知识点: 试题来源: 解析 √ 反馈 收藏
百度试题 题目在SQL中, ___约束的关键字为primary key, ___约束的关键字为foreign key。相关知识点: 试题来源: 解析 错 反馈 收藏
了解SQL中的PRIMARY KEY和FOREIGN KEY约束是数据库设计中的关键。首先，让我们解析这两者的基本概念及其使用方式。PRIMARY KEY约束用于在数据表中标识唯一且不可重复的记录。每个表最多只有一个PRIMARY KEY，它确保数据的唯一性和完整性。创建或修改表时可添加此约束。语法示例展示了在创建表时添加PRIMARY K...
Primary key is used as a unique record identity in a table, primary key usually also be indexed, to support quick search based on the column used as a primary key. A primary key does not depend on any other key, be it in the same table, or a different one. A foreign key...
To understand primary & foreign key concept in depth with the following example : Click Here – Get SQL Training with Real-Time Projects Creation of primary key in the new table : “Student” table : idnameclassAge 1samirFYBA25 2ankitFYSC25 ...
FOREIGN KEY (字段1) REFERENCES 外表(字段1) ) 创建Orders表,外键pId,指向Persons表的pId CREATE TABLE Orders(O_Id int NOT NULL,OrderNo int NOT NULL,pId int,PRIMARY KEY (O_Id),FOREIGN KEY (pId) REFERENCES Persons(pId)) 如需定义多个列的 FOREIGN KEY 约束,使用下面的 SQL 语法 ...
A primary key is defined as a column or a group of column that their value are always be unique. Normally, NULL value will never be allowed in this co
1. 数据库有六大约束 主键(primary key) 外键(foreign key):被参照的键必须有唯一约束或是主键 非空(not null) 默认(default) 检查(check):oracle独有 唯一(unique) 2. 六大约束的用法 以下所有演示的SQL语句都是基于Oracle,
test=# alter table tbl_foreign add constraint fk_tbl_foreign_a_b foreign key(a,b) references tbl_foreign_refd(a,b) match simple on delete no action on update no action; 1. 测试例1.match simple on delete no action on update no action ...
SQL statement is: CREATE TABLEUSERS( user_idSMALLINTNOT NULLPRIMARY KEY, user_nameVARCHAR(50), ) OR CREATE TABLEUSERS( user_idSMALLINTNOT NULL , user_nameVARCHAR(50), PRIMARY KEY(user_id) ) Foreign key is use to referential to the unique parent table. ...