Use of Oracle database objects

If a worker wants to do a good job, he must sharpen his tools first
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One 、 Sequence

Sequences can be used in automatic growth columns of database tables , If our students watch id Want to 1 Start , And then automatically grow , Each time 2, That is, students id yes 1、3、5、7、9 Such , We can use it with sequences
The sequence has the following properties
sequence_name： Sequence name
min_value： The minimum value of the current sequence
max_value： The maximum value of the current sequence
increment_by： The step size of each sequence increase
cy： Whether it is a cyclic sequence
or： Do you need to sort
cache_size： Number of caches , The default is 20 individual
last_number： The last value
nextval： Get the next content of the sequence , The value of the sequence increases with each call
currval： Indicates the current content of the sequence , Each call sequence will not grow

1、 Create a sequence

create sequence myseq;

2、 Insert a piece of data into the student table , Student id Use myseq Sequence

insert into student(id,name) values (myseq.nextval;' Zhang San ');

3、 change myseq The step size of the sequence , Increase every step 2

create sequence myseq increment by 2;

4、 change myseq The starting value of the sequence is 10000

create sequence myseq increment by 2 start with 10000;

5、 Create a cyclic sequence , And don't use caching

If we want a column of data to be just 1 To 9 The data of , Then we can use a cyclic sequence to operate

create sequence myseq
minvalue 1 maxvalue 9
cycle nocache;

Two 、 The function of synonyms

Synonyms can give a table of one schema to another schema to access .

1、 take scott Under the user student Table synonymous to sys The user to use

create sysnoym student for scott.emp;

2、 take scott Under the user student Table synonyms are for all users

create public sysnoym student for scott.emp;

3、 ... and 、 Definition and use of views

Views are designed to simplify complex queries , The view is a virtual table , It doesn't store data , But the data comes from real tables

1、 Create a view , From the student list, the name is ‘ Zhang San ’ Of students

create view studentview as select * from student where name = ' Zhang San ';

2、 Query student view

select * from studentview;

3、 Update student view , take name by ‘ Zhang San ’ The age of is updated to 20

update studentview set age = 20 where name = ' Zhang San ';

At this time, we found the real table student The age of Zhang San has also been revised , So changing the view in this way will affect the data of the real table , Then let's create a view so that its modification will not affect the real table .

4、 Create a view , From the student list, the name is ‘ Zhang San ’ Of students , And modifying the view cannot affect the data of the original real table

create or replace view studentview as 
select * from student where name = ' Zhang San '
with check option; 

5、 Create a view , From the student list, the name is ‘ Zhang San ’ Of students , And the view is set to read-only

create or replace view studentview as 
select * from student where name = ' Zhang San '
with read only;

Four 、 Definition and use of index

1、 Create a student table , And give name Index

create index name_index on student (name);

5、 ... and 、 summary

The relevant contents here have not been sorted out yet , The article continues to be updated later , Recommended collection .

The commands involved in the article must be typed several times each like me , Only in the process of knocking can you find out whether you really master the command .

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