RELATION (relational database) vs RELATIONSHIP (E-R model)FK: [many side] dependent ---> [one side] parentKeys usually are used as indexes to speed up the response to user queries INTEGRITY CONSTRAINTS Domain Constraints Allowable values for an attribute. Entity...
A relational table is a table of columns or fields that describe a listing (or rows) of data, similar to an Acoustic Campaign database. For example, a relational table may contain fields such as customer ID, transaction number, product purchased, product
其中VarName是关系的名字;RelationType指定关系类型,可以是一下四个常量之一:self::BELONGS_TO,self::HAS_ONE,self::HAS_MANYandself::MANY_MANY;ClassName是此 AR 类所关联的 AR 类的名字;ForeignKey指定关系中使用的外键(一个或多个)。额外的选项可以在每个关系的最后指定(稍后详述)。 以下代码演示了怎样定义Us...
Before I go into the details of different relationship types, I want to explain one thing. Unlike the database, an application domain object model always has a primary object that the application has fetched from the database and that is therefore the starting point for the ...
Summary: The New Object/Relational Database Design (Nordic), like many tools, is not the most fitting or expedient solution for every kind of database problem. However, the object/relational hybrid model can provide more power, greater flexibility, better performance, and even higher data ...
Each table of a relational database contains one or more data categories in column, and each___contains a unique instance of data fbr the categories defined by the columns. 每一个表的关系数据库中的列包含一个或多个数据种类,每一行包含各列定义的唯一数据实 例 相关知识点: 试题来源: 解析 t...
One RDS DB instance can be associated with multiple security groups, and one security group can be associated with multiple RDS DB instances. Too many security group rules will increase the first packet latency. You are advised to create no more than 50 rules for each security group. To enabl...
One RDS DB instance can be associated with multiple security groups, and one security group can be associated with multiple RDS DB instances. Too many security group rules will increase the first packet latency. You are advised to create no more than 50 rules for a security group. ...
The rows that satisfy the conditions of a query are called the result set. The number of rows returned in a result set can be zero, one, or many. A user can access the data in a result set one row at a time, and a cursor provides the means to do that. A cursor can be thought...
Creating a relational database model for a large organization is not a trivial task. It can take several iterations to define tables to match the characteristics described above. Sometimes you have to split an entity into more than one table. This process is callednormalization. ...