1. 外键 外键(foreignkey)以及参考完整性限制(referentialintegrity)可以让你制定表格中资料间的约束,然后将约束(constraint)加… www.360doc.com|基于451个网页 2. 外健 ... 一种是主键(PrimaryKey)关联, 一种是外健(ForeignKey)关联. 在主键关联的情况下, 显然必须有一个主键是根据别一个主键而 … ...
To access this dialog box, open the table definition for the table with the foreign key, right-click the table definition grid, and click Relationships. Options Selected Relationship Lists existing relationships. Select a relationship to show its properties in the grid to the right. If the list...
The primary key in the Customers table is CustomerNo, and the primary key in the Orders table is OrderNo. The primary key uniquely identifies the table and contains the value that the foreign key refers to. Primary keys must be unique to each row of data. In the Orders table, the Custo...
You're looking to parse a database schema and data to determine which tables are relevant or should be related to each other, without any strict definition of the relationship. In effect, you're trying to infer a relationship. I see two ways that you can infer such a relationship. First ...
There's table of Provisions that have names and IDs. Anything called an "ID" here is a surrogate key in a table. We then have Forms, FormBenefits, and Riders. Those are very different kinds of things, each in its own table, but each can have selected provisions. All the provisions...
A system includes reception of a request to check a foreign key definition associated with a database table, determination of a first foreign key relation of the foreign key definition, determination of whether the database table is a foreign key relation table identified in the first foreign ...
Foreign key constraints (also known as referential constraints or referential integrity constraints) enable definition of required relationships between and within tables.
also permits fast access to data when the primary key is used in queries. If a primary key constraint is defined on more than one column, values can be duplicated within one column, but each combination of values from all the columns in the primary key constraint definition must be unique....
also permits fast access to data when the primary key is used in queries. If a primary key constraint is defined on more than one column, values can be duplicated within one column, but each combination of values from all the columns in the primary key constraint definition must be unique....
ntroduction to MySQL foreign key A foreign key is a field in a table that matches another field of another table. A foreign key places constraints on data in the related tables, which enables MySQL to maintain referential integrity. Let’s take a look at the following database diagram in ...