Question

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Fragmentation of id's (auto_increment column) in mysql

I have this column in my database. Let’s say its name is ‘threadid’.
It contains unique ids given to each thread for distinction.

threadid
9
8
7
6
5
4
3
2
1

Let’s say I have deleted threads with id 5 and 6.

threadid
9
8
7
4
3
2
1

But when there is a submission after the deletion, the unique id given to that thread is 10. not 5. I think this is not neat.

How do I get the least possible value in the column? (in this case, 5.)

I think I can get the minimum value of the column using MIN() and keep +1 until I get the unused, unique value, but I think that’s too complicated.

Is there any simple way to do this?

Thanks.

Answer 1

I agree with the rest of everyone where it is a very bad idea to implement your own find minimal open number. But at where I work, we are given a closed set of number and when a number is free up, we must reuse.

Here is how we did it.

We do not delete the row, but set all values of every column null, So what you do is
SELECT min(id) WHERE columnA IS NULL, and if this returns something, we reuse, otherwise, insert a new row.