How do I reset sequence numbers to become consecutive?

Question

I\'ve got a mysql table where each row has its own sequence number in a \"sequence\" column. However, when a row gets deleted, it leaves a gap. So...

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Answer 1

This is a question that often I read here and in other forums. As already written by zerkms this is a false problem. Moreover if your table is related with other ones you'll lose relations.

Just for learning purpose a simple way is to store your data in a temporary table, truncate the original one (this reset auto_increment) and than repopulate it.

Silly example:

create table seq (
id int not null auto_increment primary key,
col char(1)
) engine = myisam;

insert into seq (col) values ('a'),('b'),('c'),('d');

delete from seq where id = 3;

create temporary table tmp select col from seq order by id;

truncate seq;

insert into seq (col) select * from tmp;

but it's totally useless. ;)