Oracle fundamentals summary

Oracle Database introduction

1.Oracle It's a relational database , Multi user support 、 Transaction processing of large amount of business . Oracle client-based 、 Server side . Distributed 、 portable .
2. The collection of background processes and memory structures that manage databases is called Oracle example
3.Oracle The memory structure of contains the following two memory areas ： System global area (SGA) 、 Program global area (PGA)
4.Oracle The default user ,SYS Super administrator ,SYSTEM General administrator ,SCOTT Ordinary users （ Many authorities have no , need SYSTEM to ）.

Windows Medium Oracle service

ORACLE The database has the following characteristics

1、Oracle Cross platform , portable
2、 Data security and integrity control
3、 Multi user support 、 Transaction processing of large amount of business
4、 Support distributed data processing

The creation of a table 、 Modify and delete

1. A tablespace is the largest logical unit in a database , One Oracle The database contains at least one table space , It's called System System space for .
2. Data definition language （DDL）： create、 alter 、drop
   Data manipulation language （DML）：insert、select、 detele、 update、 truncate
   Transaction control language （TCL）：commit、 rollback、 savepoint
   Data control language （DCL）： grant、 revoke

data type

1. Character

data type	Value range （ byte ）	explain
varchar2	0~4000	Variable length string
nvarchar2	0~1000	Used to store unicode Variable length character data of character set
char	0~2000	Used to describe fixed length character data
nchar	0~1000	Used to store unicode Fixed length character data of character set
long	0~2GB	Used to store variable length strings

2. Numerical type

data type	Value range	explain
number(p,s)	p The maximum accuracy is 38 position （ Decimal system ）	p It represents precision ,s Represents the number of decimal places reserved ; Can be used to store fixed length integers and decimals
float	Used to store 126 Bit data （ Binary system ）	The stored precision is calculated in binary , The precision range is binary 1~126, To convert to binary, you need to multiply by 0.30103

3. Date type

data type	explain
date	Used to store date and time , Accurate to seconds
timestamp	The displayed date is larger than date More precise , Accurate to decimal seconds , It can also display morning or afternoon

4. Other data types

data type	Value range （ byte ）	explain
blob	Can be stored at most 4GB	Store the image 、 voice 、 Video and other binary data
clob	Can be stored at most 4GB	Store string data
bfile	Size depends on the operating system	It is used to store unstructured binary data in operating system files outside the database

Field 、 Data addition, deletion and modification

constraint