Oracle database objects

1. Introduction to database objects

• Oracle Database objects are also called schema objects , yes Oracle The database gets components commonly used create Command to create , Use alter Command to change , use drop Delete
• Database objects are collections of logical structures , The most basic database objects are tables
• Other database objects include ：

1. A synonym for 2. Sequence 3. View 4. Indexes

• Common database objects are users 、 surface 、 View 、 Indexes 、 function 、 stored procedure 、 trigger 、 Sequence 、 Synonyms, etc , as well as Oracle Unique table spaces

2. A synonym for

What is a synonym
A synonym for （Synonym） Is an alias of the database object ,Oracle It can be a watch 、 View 、 Sequence 、 The process 、 function 、 Specify an alias for database objects such as packages .

The function of synonyms
A synonym is an alias for an existing object .

1. simplify SQL sentence
2. Hide the name and owner of the object
3. Provide public access to objects

Synonym classification
There are two types of synonyms ：

1. Public synonyms can be accessed by all database users .
2. Private synonyms can only be accessed within their schema , And cannot have the same name as the object in the current mode .

2.1 Private synonyms

Create private synonyms

• The administrator grants ordinary users the right to create private synonyms ：grant create synonym to user name ;
• Create Syntax ：create synonym Alias for user name . Table name
  
  Case study ：

-- to scott Tabular emp Table create private synonyms sa
create synonym sa for scott.emp;

-- Call private synonyms select * from  Alias 
select * from sa;

2.2 Common synonyms

Create common synonyms

• The administrator grants common users the right to create common synonyms ：grant create public synonym to user name ;
• Create Syntax :create public synonym Alias for user name . Table name ;
  
  Case study ：

-- to scott Tabular emp Table create common synonyms sb
create public synonym sb for scott.emp;

-- call 
-- Synonym owner select * from  Alias 
select * from sb;

-- Call the common synonyms of other users ：
-- The common synonym owner grants the caller permission ：grant all on  Table name  to  user name ;
-- such as ：
grant all on emp to sb;-- grant sb User access emp All permissions of the table ;

2.3 Delete existing synonyms

Delete synonyms

• Delete private synonyms ：drop synonym user name . Synonym name ;
• Delete common synonyms ：drop public synonym user name . Table name ;

When deleting common synonyms, ordinary users need to be authorized by the administrator to delete common synonyms ：grant drop public synonym to user name ;

3. Sequence

• Sequences are used to generate unique 、 Objects with consecutive numbers
• The sequence can be ascending , It can also be in descending order
• Use CREATE SEQUENCE Statement to create a sequence

create sequence se_01 -- Create sequence name
start with 10 -- Set sequence from 10 Start
increment by 10 -- Set each increase 10( The interval between serial numbers is 10)
maxvalue 2000 -- Set the maximum sequence number to 2000
minvalue 10 -- Set the minimum sequence number as 10
nocycle
cache 10;

3.1 Create default sequence

• Sequence sequence： Used to generate continuous 、 Unique serial number
• Create a simple sequence ： initial value =1, The incremental =1
  grammar ：create sequence The sequence of ;

3.2 Delete sequence

Delete sequence

• grammar ：drop sequence The sequence of ;
  create sequence SEQ_NO;

select SEQ_NO.NEXTVAL from dual;
select SEQ_NO.CURRVAL from dual;

insert into hrit values(SEQ_HRIT.NEXTVAL,‘john’);

select * from hrit;

3.3 Usage sequence

– Sequence name .nextval The next value is
– grammar ： Sequence name .currval Current value
select seq_xxx.currval from dual;

Batch query sequence
– grammar ：select The sequence of .nextval from Table name ;
select seq_xxx.nextval from emp;

Create complex sequences
– Create sequence
– grammar ：create sequence The sequence of
create sequence seq_aaa

Change and delete sequences

4. View

1. View concept :

• Views display data from one or more tables in a customized manner
• Views can be thought of as “ Virtual table ” or “ Stored queries ”
• The table on which the view is created is called “ Base watch ”

2. The advantages of view are ：

• Provides another level of table security
• The complexity of hidden data
• Simplified user's SQL command
• Change of isolation base table structure
• By means of rebranding , Provide data from another perspective

Create view ：

-- combination emp Table and dept Table to find out the name of each employee + Position + salary + Department number + Department name , And create views .
create view v_01
as
select ename,sal,job,a.deptno,dname from emp a 
inner join dept b
on a.deptno=b.deptno;

Call view ：select * from View name ;

5. Indexes

• To improve SQL The performance of statement execution
• Reduce disk I/O
• Use CREATE INDEX Statement to create an index
• Data that is logically and physically independent of the table
• Oracle Automatically maintain indexes
• There are various types of indexes , In addition to the standard index , There are also some special types of indexes ： unique index 、 Bitmap index 、 Composite index 、 Function based index 、 Reverse key index

• Create index Syntax ：create Index type index Index name a on Table name ( Name )
  unique index ：create unique index insex_01 on ta_01(sid);

Reverse key index

• Reverse key index reverses each byte of the key value of the index column
• Usually based on columns whose values are growing continuously , Distribute data evenly across the index
• Use... When creating an index REVERSE keyword
  

-- Index page ： The address where the data is stored （ Indexes ）
--  Data pages ： Details of stored data 
  
-- Create the appropriate index ：
--a- Large amount of data 
--b- Usually used for where Conditions 、 grouping 、 Index the sorted fields 

create table test(
 id number,
 name varchar2(50)
)

select * from test where name='JACK4000000';
--Oracle Index classification ：
--a- Standard index 
--create index  Index name  on  Table name ( Name );
create index ix_name on test(name);

--b- unique index , Primary key 、 Unique key automatically applies a unique index 
-- create unique index  Index name  on  Table name ( Name );

--c- Composite index , For multi condition combined query  
-- create index  Index name  on  Table name ( Name 1, Name 2...);
  create index ix_name on test(name,age);
  
-- Delete index 
--drop index  Index name ;
-- Insert 5000W Data 

create sequence seq_test;

truncate table test;

declare 
       nums number:=1;
begin
  loop
  insert into test values(seq_test.nextval,'JACK'||nums);
  nums:=nums+1;
  if nums=50000000 then
    exit;
  end if;
  end loop;

summary

• Synonyms are aliases for existing database objects
• Sequences are used to generate unique 、 Consecutive serial numbers
• A view is a virtual table based on one or more tables
• An index is an optional structure related to a table , For improvement SQL The performance of statement execution
• Index types have standard indexes 、 unique index 、 Reverse key index 、 Bitmap index and function based index
• Index organization table accesses data based on primary key