Oracle Getting Started fifth day (bottom)--Database other objects

I. Overview

　Other database objects

　　

　　The main mastery is the sequence

Second, sequence

　1. What is a sequence

　　Sequence: A database object that can be used by multiple users to produce unique values

Automatically provide a unique value

Shared objects

　　　　Primarily used to provide primary key values

Loading sequence values into memory can improve access efficiency

　　2. Create a sequence

CREATESEQUENCE SEQUENCE[INCREMENT by N]  --the value of each increment       [START with N]    --from which value to start       [{MAXVALUE N | Nomaxvalue}]       [{MINVALUE N | Nominvalue}]       [{CYCLE | Nocycle}]     --whether a loop is required       [{CACHE N | NOCACHE}];--whether to cache login

　　There are two main ways of using the sequence:

Nextval Returns the next valid value in the sequence that any user can reference

current value of the stored sequence in the Currval

Nextval should be specified before Currval, both should be valid at the same time

SELECT  from dual;    Nextval----------       101

　　To create a sequence example:

CREATEby1 with 10086  2

　　Examples of Use:

INSERT  into VALUES (Emp_seq.nextval,' Xiao Ming ');

　　Note : The sequence appears cracked in the following cases:

Rollback (the sequence is obsolete after rollback, no longer used)

System exceptions

Multiple tables use the same sequence at the same time

　　　3. View the sequence

Select  from user_sequences;

　4. Modifying the sequence

ALTER SEQUENCE dept_deptid_seq                 by  - 999999 NOCACHE               nocycle;                 

　　5. Deleting a sequence

DROP SEQUENCE Dept_deptid_seq;

　　for more detailed sequence use, refer to : https://www.cnblogs.com/always-online/p/4029703.html

http://blog.csdn.net/java958199586/article/details/7360152

Third, index

　　　　1. Introduction to the Index

　　　　

　　For more index usage analysis, refer to the MySQL Index Analysis section : http://www.cnblogs.com/jiangbei/p/7420136.html

　　　2. Create an index

CREATE INDEX Index  on Table (column[, Column]...);

　　Note: Primary keys and UNIQUE constraints will automatically create an index

Example:

CREATE INDEX  on EMP5 (name)

　　　　3. View Index

SELECT     ic.index_name, Ic.column_name,    ic.column_position col_pos,ix.uniquenessfrom     User_indexes IX, User_ind_columns ICWHERE    =  ix.index_name and    ='EMPLOYEES';

　　　　4. Deleting an index

DROP INDEX index;

iv. synonyms synonym

　　Create:

CREATE [public] synonym synonym  for    Object

Example:

CREATE  for employees;

　Delete:

DROP Synonym D_sum;

Oracle Getting Started fifth day (bottom)--Database other objects