Retrieval operations in relational databases are composed of what three basic operations

#The retrieval operations of relational databases are composed of three basic operations: selection, projection and join.

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Introduction to relevant knowledge points:

Relational database is the mainstream of database applications, and many database management The data model of the system is developed based on the relational data model.

1. Relational database

In a given application field, the collection of all entities and the relationships between entities constitutes a relational database.

2. Types and values ​​of relational databases

The type of relational database is called the relational database schema, which is a description of the relational database, the definition of several fields, and several relationships defined on these fields. Schema; the value of a relational database is the collection of relationships corresponding to these relational schemas at a certain moment, usually referred to as a relational database for short.

The oracle database belongs to Oracle Corporation (the Chinese name is Oracle Corporation), as well as SQL, access; db2 belongs to IBM (the Chinese name is International Business Machines Corporation). Mainstream relational databases include Microsoft's Sql server, Sybase's sybase, (Informix) software company's informix, and free MySQL.

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