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This article mainly introduces what is the structure of the relational model in the database table, which has a certain reference value. Interested friends can refer to it. I hope you will gain a lot after reading this article.

The order of the records in a relational database table can be reversed arbitrarily without affecting the actual meaning of the data in the database. There are multiple records in the table of a relational database, and the order of the records will not affect the data relationship in the database, so the order of rows is indifferent and can be reversed at will.

The order of the records in a relational database table can be reversed arbitrarily without affecting the actual meaning of the data in the database.

Relational database is a database based on relational database model. The definition of a relational database results in a table of metadata or a formal description of tables, columns, ranges, and constraints. Each table (sometimes referred to as a relationship) contains one or more types of data represented by columns. Each row contains a unique data entity, which is the category defined by the column.

Relational model structure

1. Single data structure-relationship (table file). Tables in relational databases use two-dimensional tables to store data, which is a logical group with relevant information arranged by rows and columns, which is similar to Excel worksheets. A database can contain any number of tables.

From the user's point of view, the logical structure of a relational model is a two-dimensional table, consisting of rows and columns. This two-dimensional table is called a relationship. In popular terms, a relationship corresponds to a table.

2. Tuple (record). A row in a table is a tuple, or a record.

There can be multiple records in the table, and the order of the records does not affect the data relationship in the library, so the order of rows is indifferent and can be reversed at will.

3. Attributes (fields). Each column in the data table is called a field, and the table is defined by the various fields it contains. Each field describes the meaning of the data it contains. The design of the data table is actually the design of the field. When you create a data table, you assign a data type to each field and define their data length and other properties. Fields can contain a variety of characters, numbers, and even graphics. Like a mistake! The reference source was not found.

4. Attribute value. The intersection of rows and columns indicates an attribute value, for example, "Database principle" is the attribute value of the course name.

5. Main code. A master code (also known as a primary key or primary keyword) is the data in a table that is used to uniquely determine a tuple. Keyword is used to ensure the uniqueness of records in a table, can be one or more fields, and is often used as an index field for a table. Each record has a different keyword, so it can uniquely identify a record. The keyword is also called the primary keyword, or primary key for short. Like a mistake! The reference source was not found.

6. Domain. The range of values for the property.

7. Relationship model. The description of a relationship is called a relational schema. The description of the relationship is generally expressed as: relationship name (attribute 1, attribute 2. Attribute n). For example, the above relationship can be described as: course number, course name, credits, teacher).

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