Referential Integrity • Ensures that a value that appears in one relation for a given set of attributes also appears for a certain set of attributes in another relation. • Example: If “Perryridge” is a branch name appearing in one of the tuples in the account relation, then there exists a tuple in the branch relation for branch “Perryridge”. • Primary and candidate keys and foreign keys can be specified as part of the SQL create table statement: • The primary key clause lists attributes that comprise the primary key. • The unique key clause lists attributes that comprise a candidate key. • The foreign key clause lists the attributes that comprise the foreign key and the name of the relation referenced by the foreign key. By default, a foreign key references the primary key attributes of the referenced table用中文详细讲解以上内容和相关知识点
时间: 2024-04-28 15:22:01 浏览: 99
参照完整性是数据库设计中的一个概念,它确保了表之间的关系正确地维护。它保证了如果一个值在一个表的属性中出现,它也必须在另一个表的属性中出现,其中它作为外键被引用。
例如,如果账户关系中包含一个分行名称为“Perryridge”的元组,则分行关系中必须存在一个具有相同分行名称的元组。
主键、候选键和外键用于唯一地标识表中的元组,并且外键用于引用另一个表中的元组。在 SQL 中,可以使用创建表语句来指定这些键。
主键子句列出组成主键的属性,这些属性可以唯一地标识表中的每个元组。唯一键子句列出组成候选键的属性,这是一组属性,也可以唯一地标识表中的每个元组。
外键子句列出组成外键的属性和引用外键的表的名称。默认情况下,外键引用被引用表的主键属性。
总体而言,参照完整性通过强制执行表之间的关系来确保数据库中数据的一致性和准确性。
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Referential Integrity • Ensures that a value that appears in one relation for a given set of attributes also appears for a certain set of attributes in another relation. • Example: If “Perryridge” is a branch name appearing in one of the tuples in the account relation, then there exists a tuple in the branch relation for branch “Perryridge”. • Primary and candidate keys and foreign keys can be specified as part of the SQL create table statement: • The primary key clause lists attributes that comprise the primary key. • The unique key clause lists attributes that comprise a candidate key. • The foreign key clause lists the attributes that comprise the foreign key and the name of the relation referenced by the foreign key. By default, a foreign key references the primary key attributes of the referenced table详细讲解以上
Referential Integrity is a concept in database design that ensures that the relationships between tables are maintained correctly. It ensures that if a value appears in one table's attribute, it must also appear in another table's attribute where it is referenced as a foreign key.
For example, if the account relation contains a tuple with a branch name of "Perryridge", there must be a corresponding tuple in the branch relation with the same branch name.
Primary keys and candidate keys are used to uniquely identify tuples in a table, and foreign keys are used to reference tuples in another table. In SQL, these keys can be specified using the create table statement.
The primary key clause lists the attributes that make up the primary key, which uniquely identifies each tuple in a table. The unique key clause lists the attributes that make up a candidate key, which is a set of attributes that can also uniquely identify each tuple in a table.
The foreign key clause lists the attributes that make up the foreign key and the name of the referenced table. By default, a foreign key references the primary key attributes of the referenced table.
Overall, referential integrity ensures the consistency and accuracy of data in a database by enforcing the relationships between tables.
referential integrity
参照完整性是指在数据库中,所有的外键必须引用到已经存在的主键上,以保证数据的一致性和完整性。如果外键引用的主键不存在,或者主键被删除了,那么就会违反参照完整性,导致数据不一致或者不完整。因此,参照完整性是数据库设计中非常重要的一个概念。