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Re: How to generate sequence in MySql
Posted by: Andy Salnikov
Date: January 23, 2009 05:38PM

I had just to implement "sequence" myself, here is my example (I did check few other examples but could not find one that has concurrency support, so I chose to invent one more). I did not try to emulate exactly Oracle or Postgres syntax for sequences, I only need one sequence per database. Anyway the result is pretty close to what Postgres does.

And it uses auto-increment column for implementation, of course, as this is the only way in mysql to satisfy concurrency requirements. Here it is:


delimiter %%

drop table if exists R_ObjectId_seq_tbl %%
create table R_ObjectId_seq_tbl ( nextval bigint not null primary key auto_increment ) engine = MyISAM %%

drop function if exists R_ObjectId_nextval %%
create function R_ObjectId_nextval()
returns bigint
begin
insert into R_ObjectId_seq_tbl values (NULL) ;
set @R_ObjectId_val=LAST_INSERT_ID() ;
delete from R_ObjectId_seq_tbl ;
return @R_ObjectId_val ;
end
%%

drop function if exists R_ObjectId_currval %%
create function R_ObjectId_currval()
returns bigint
begin
return @R_ObjectId_val ;
end
%%

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Re: How to generate sequence in MySql
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