MySQL Realizes Sequence Similar to Oracle

MySQL implements a sequence similar to Oracle

Oracle1 uses sequences (Sequence) to handle primary key fields, while MySQL provides self-growth (increment) for similar purposes;

However, in the actual use process, it is found that the self-growth of MySQL has many drawbacks: it can't control the step size, start indexing, whether it is circular or not, etc.; If you need to migrate the database, it is also a big problem for the primary key.

This paper records a scheme to simulate Oracle sequence, with emphasis on ideas and code second.

The use of Oracle sequence is nothing more than the use of. nextval and.currval pseudo-columns. The basic idea is:

1. Create a new table in MySQL to store sequence names and values;

2. Create a function to get the values in the sequence table;

The details are as follows:

The table structure is:

drop table if exists sequence;  
create table sequence (  
  seq_name    VARCHAR(50) NOT NULL, --  Sequence name   
  current_val   INT     NOT NULL, -- Current value   
  increment_val  INT     NOT NULL  DEFAULT 1, -- Step length ( Span )  
  PRIMARY KEY (seq_name)  
);

Simulation scheme for realizing currval

create function currval(v_seq_name VARCHAR(50))  
returns integer 
begin 
  declare value integer;  
  set value = 0;  
  select current_value into value  
  from sequence 
  where seq_name = v_seq_name;  
  return value;  
end;

Function is used as: select currval('MovieSeq'); 

Simulation scheme for realizing nextval

create function nextval (v_seq_name VARCHAR(50))  
return integer 
begin 
 update sequence 
 set current_val = current_val + increment_val  
 where seq_name = v_seq_name;  
 return currval(v_seq_name);  
end;

Function is used as: select nextval('MovieSeq');  


Function to increase setting value

create function setval(v_seq_name VARCHAR(50), v_new_val INTEGER)  
returns integer 
begin 
 update sequence 
 set current_val = v_new_val  
 where seq_name = v_seq_name;  
return currval(seq_name);

Similarly, the function of step size operation can be added, which will not be described here.

Pay attention to the syntax, and the database fields should correspond to the

use bvboms; 
DELIMITER $$ 
create function setval(v_seq_name VARCHAR(50), v_new_val INTEGER) 
returns integer 
begin 
 update sequence 
 set current_val = v_new_val 
 where seq_name = v_seq_name; 
return currval(seq_name);
end $$
DELIMITER $$

Summarize