How to fill in the “holes” in auto-increment fields?

Question

I\'ve read some posts about this but none cover this issue.

I guess its not possible, but I\'ll ask anyway.

I have a table with more than 50.000 registers. I

Answer 1

There is a simple way but it doesn't perform well: Just try to insert with an id and when that fails, try the next one.

Alternatively, select an ID and when you don't get a result, use it.

If you're looking for a way to tell the DB to automatically fill the gaps, then that's not possible. Moreover, it should never be necessary. If you feel you need it, then you're abusing an internal technical key for something but the single purpose it has: To allow you to join tables.

[EDIT] If this is not a primary key, then you can use this update statement:

update (
    select *
    from table
    order by reg_id -- this makes sure that the order stays the same
)
set reg_id = x.nextval

where x is a new sequence which you must create. This will renumber all existing elements preserving the order. This will fail if you have foreign key constraints. And it will corrupt your database if you reference these IDs anywhere without foreign key constraints.

Note that during the next insert, the database will create a huge gap unless you reset the identity column.