How to create an auto-increasing primary key in Oracle

How Oracle creates a self-increasing primary key

Oracle primary keys are commonly divided into UUID and There are two types of self-increasing int. Let’s briefly talk about their respective advantages and disadvantages:

Advantages of UUID

1. It is easy to generate, whether it is through UUID can be easily created using sys_guid() or java's uuid.

2. Suitable for insert and update operations in batch data.

3. Cross-server data merging is very convenient.

Advantages of INT self-increasing

1. Small space occupied

2. Good performance, UUID is not on the same level as int

3. Easy to remember

Their respective advantages are each other’s shortcomings

Recommended "mysql video tutorial"

Applicable Scope:

Generally, UUID is used as the only primary key in a distributed environment. As for other projects, I strongly recommend using int as the primary key.

PS: Recently, one of my distributed projects also had UUID duplication during the peak weekend access period, so I did not write down the advantage of UUID as a globally unique ID, but we can use Zookeeper as the primary key to generate it. The operator creates a unique primary key of type int, which is completely fine.

So to sum up, I still recommend that all primary keys should use the int type. The advantages of the int type are particularly obvious when it comes to tens of millions of data.

Oracle steps to create self-increasing:

Create self-increasing sequence

-- 创建自增长序列
create sequence seq_on_chance_contract
increment by 1 -- 每次加1
start with 1 -- 从1开始计数
nomaxvalue -- 不设置最大值
nocycle -- 一直累加
nocache;

Create data table

The primary key can Use INTEGER and NUMBER. If the system uses Hibernate as the ORM framework, it is not recommended to use NUMBER

create table TBL_CHANCE_CONTRACT
(
  ID                INTEGER  PRIMARY KEY,
  CHANCE_SUCCESS_ID VARCHAR2(50) not null,
  CONTENT           CLOB,
  CREATE_USER_ID    VARCHAR2(50),
  CREATA_USER_NAME  VARCHAR2(80),
  CREATE_DATE       TIMESTAMP(6)
)

Create a primary key trigger so that you do not need to manage the ID primary key when adding new records

-- 创建主键触发器  
CREATE OR REPLACE TRIGGER tg_on_id_chance_contract 
       BEFORE INSERT ON TBL_CHANCE_CONTRACT FOR EACH ROW WHEN (new.ID is null)
BEGIN
       SELECT seq_on_chance_contract.nextval into:new.ID from dual;
END;

Some tips ：

View all sequences and tables

-- 查找所有SEQUENCE、TABLE
select * from user_objects ubs;
-- 查找所有SEQUENCE
select * from user_objects ubs where ubs.OBJECT_TYPE='SEQUENCE';

Check the current sequence number

select seq_on_chance_contract.nextval from dual;
select seq_on_chance_contract.currval from dual;

Reset sequence

General reset The sequence needs to be deleted and then rebuilt, but this is more troublesome. There are two ways to do it without deleting the sequence:

1. Use the step parameter to first find out the nextval of the sequence. Remember, put Incrementally change the value to negative (and vice versa), and then change it back again.

Assume that the sequence name that needs to be modified is seq_on_chance_contract

-- 重置序列
select seq_on_chance_contract.nextval from dual;        -- 假设得到结果 n
alter sequence seq_on_chance_contract increment by -2;  -- 注意是 -(n-1) 
select seq_on_chance_contract.nextval from dual;        -- 再查一遍，走一下,重置为1了 
alter sequence seq_on_chance_contract increment by 1;   -- 还原

2. Use the stored procedure to implement (v_seqname)

create or replace procedure seq_reset(v_seqname varchar2) as n number(10); 
tsql varchar2(100); 
begin 
execute immediate 'select '||v_seqname||'.nextval from dual' into n; 
n:=-(n-1); 
tsql:='alter sequence '||v_seqname||' increment by '|| n; 
execute immediate tsql; 
execute immediate 'select '||v_seqname||'.nextval from dual' into n; 
tsql:='alter sequence '||v_seqname||' increment by 1'; 
execute immediate tsql; 
end seq_reset;

Then call the stored procedure:

exec seq_reset('v_seqname');

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