Oracle Database Learning (1)-Basic knowledge

Knowledge Points:

1.Oracle database is a relational database management system developed by Oracle (Oracle/shen Domain), which is one of the most widely used databases in the world at present.

The main version is oracle9i,oracle10g,oracle11g,oracle12c; the database that the enterprise uses most is oracle10g;

Oracle saves data in a table as a storage unit;

2. Table Space

1 table space is the storage of database objects (tables, views, indexes, sequences ...). containers, tables and table spaces are like the relationships between documents and documents;

2 table space can be composed of one or more folders, these databases are the actual location of data stored in the database;

3 Every time the database is created, the system will create a table space by default, a database can have a number of table space, or can only have a system table space;

3.Oracle Common Database types

1 char (n): Used to mark a fixed-length string, n represents the maximum number of strings that can be saved. When the number of actual saved strings is less than n, the space is used to complement the whole;

such as: char (10), save ' Liu ', will actually occupy 10 storage space, waste 7 storage space

2) varchar (n): Used to save variable length strings, when the character to be saved is less than N, will be saved according to the actual character length;

such as: varchar (10), save ' Liu ', actually only occupies 3 storage space;

3) VARCHAR2 (n): Used to save variable-length strings, Oracle custom type, very good compatibility, it is recommended to use VARCHAR2 instead of varchar type;

4) Data type: number

Number (parameter 1, parameter 2): Can be used to store integers and decimals, parameter 1 represents the maximum digits of valid data, and parameter 2 indicates the maximum number of digits in a decimal;

such as: Number (3): 3-bit integer;

Number (7,2): represents 7-bit valid data, 5-bit integer, 2 decimal;

5 Date-time: Dates

Default Date: Dd-mon-yy

4.SQL statement: Structured Query Language, SQL is a special command set for operation database, powerful database language;

DDL: Database definition language, used to create, modify, and delete tables: Create, DROP, alter

DCL: Used to manage transactions in the database: Commit, rollback

DML: Language for manipulating data in a database: INSERT, UPDATE, delete

DQL: Database Query Language: SELECT