insert into query question

[Cyjm1120]

Hi I am having troubles inserting item into a table with a primary key in it.

 

My problem is that every time I added a row into a table without specifying the primary key, mysql will not add it to the next available id.

 

For example, I have 5 rows initially and I added 10 rows into my table by using the insert into query. However when I delete the 10 rows and add another row in, the id of the additional row will become 16 instead of 6.

 

FYI, this is a php page that inserts my data into the table.

[ginerjm]

Uhhh...... Where's the code?

[Jacques1]

MySQL does not magically reset the AUTO_INCREMENT counter when you delete rows. Once a number is taken, it won't be used again. This is the easiest and most robust solution.

 

If you absolutely must have this feature, you need to implement it yourself. But be aware that this is much harder than it may sound, because you have to deal with concurrent requests. For example, two rows may be inserted at (almost) the same time, in which case you must make sure that they don't take the same “next ID”.

 

My advice is, just stick to whatever number you get. An UNSIGNED INT can hold numbers up to 4 trillion, so there's not exactly a shortage of IDs. And if your application cannot handle gaps between the IDs, then that's the problem which needs to be fixed.

[Cyjm1120]

My code can handle the gaps between the IDs. I am wondering if there is any way that could make my table look better. But after listening to your advise, I will just stick with whatever id I get.

 

Thanks

[Jacques1]

Actually, you shouldn't expect AUTO_INCREMENT to yield a perfect sequence at all. There are all kinds of situations when a gap can occur. For example, if an INSERT query is aborted due to a constraint violation or a transaction rollback, then the reserved numbers will be skipped and never made available to you. You cannot even rely on the order of the numbers. You may get a low number after a high number due to a deferred query.

 

The only promise which AUTO_INCREMENT makes is that you get a unique number. The exact value depends on the underlying technical details and is more or less undefined.

Edited November 12, 2014 by Jacques1