What are the two categories of data operations in relational databases?

Data operations in relational databases are divided into queries and updates. Query statements are used for various retrieval operations, and update operations are used for operations such as insertion, deletion, and modification.

Relational database is a database based on the relational database model. It uses concepts and methods such as set algebra to process data in the database. It is also a Organized into a set of formally descriptive tables that are essentially special collections of data items that can be accessed or recalled in many different ways without the need for reorganization Database table.

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 called a relationship) contains one or more data types represented by columns. Each row contains a unique data entity of the type defined by the column.

When creating a relational database, you can define the range of possible values ​​for a data column and further constraints that may apply to that data value. The SQL language is a standard user and application interface to a relational database. The advantage is that it is easy to expand, and after the initial database creation, a new data type can be added without modifying all existing applications.

Data operations in relational databases are divided into two categories: query and update. Query statements are used for various retrieval operations, and update operations are used for operations such as insertion, deletion, and modification.

Relational query languages ​​are divided into two categories according to their different theoretical foundations:

1. Relational algebra language: query operations are based on set operations. DML language.

2. Relational calculus language: The query operation is a DML language based on predicate calculus.

Relational databases are divided into two categories:

• One is desktop database, such as Access, FoxPro and dBase, etc.;

• The other type is client/server database, such as SQL Server, Oracle and Sybase.

Generally speaking, desktop databases are used for small, stand-alone applications. They do not require a network or server and are more convenient to implement, but they only provide data access functions.

Client/server database is mainly suitable for large-scale, multi-user database management systems. The application program consists of two parts: one part resides on the client computer and is used to display information to users and interact with users; the other part Part of it resides in the server and is mainly used to implement operations on the database and calculation and processing of data.

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