Oracle database learning notes (I)

Time:2021-10-21

1. Database overview

Database (database, DB) refers to the collection of organized, shareable and large amount of data that has existed in the computer for a long time. Data is organized and stored in the database according to a specific data model.

Relational database: it is a database that stores data in the form of association relationship or two-dimensional table.

Such as Oracle, mysql, DB2, SQL server, etc;

Non relational database: it is generally a database that stores data in the form of key value pairs.

Such as redis, Hadoop (HBase), etc

2. Oracle database overview

Oracle database, also known as Oracle RDBMS, or Oracle for short. Oracle is a relational database management system. It is a leading product in the field of database. It can be said that Oracle database system is a popular relational database management system in the world. The system has good portability, convenient use and strong function. It is suitable for all kinds of large, medium and small microcomputer environments. It is a database scheme with high efficiency, good reliability and high throughput.

Note: database management system (DBMS) is a large-scale software for manipulating and managing databases, which is used to establish, use and maintain databases, referred to as DBMS for short

Relational database management system (RDBMS) refers to a set of programs (database management system software) including interrelated logical organization and access to these data. Relational database management system is a system that manages relational database and logically organizes data.

3.SQL

Here is a reference. SQL is the acronym of structured query language. SQL is a database language. Communication with Oracle server can be realized through SQL. Crud and other operations can be performed.

Note: crud refers to create, retrieve, update and delete

4. SQL classification

DDL (data definition language): data definition language, used to define tables, columns, etc;

    For example: create data table

DML (data manipulation language): data manipulation language, used to define database records (data);

    Such as adding data, modifying data and deleting data

DQL (data query language): a data query language used to query records (data).

    For example, query data

DTL (data transaction language): data transaction language, used to operate transactions.

    For example, start a transaction and commit a transaction

DCL (data control language): data control language. Used to manipulate users and permissions

    For example: create user, authorize