删除表中的行时如何更新autoincremented id？

Question

I am creating application that uses MYSQL database in C#. I want to delete row and update autoincremented value of id in table. For example, I have table with two columns: id and station, and table is station list. Something like this

id station
1 pt1
2 pt2
3 pt3

If i delete second row, after deleting the table looks something like this:

id station
1 pt1
3 pt3

Is there any way that I update id of table, for this example that id in third row instead value 3 have value 2? Thanks in advance!

Answer 1

I suggest you don't do anything special when a row is deleted. Yes you will have gaps in the ids, but why do you care? It is just an id.

If you change the value of id_station, you would also need to update the value in all tables that have an id_station field. It causes more unnecessary UPDATES.

Answer 2

An autoincrement column, by definition, should not be changed manually.
What happen if some other tables use this ID (3) as foreign key to refer to that record in this table? That table should be changed accordingly.
(Think about it, in your example is simple, but what happen if you delete ID = 2 in a table where the max(ID) is 100000? How many updates in the main table and in the referring tables?)

And in the end there is no real problem if you have gaps in your numbering.

Answer 3

The only way to change the value of the id column in other rows is with an UPDATE statement. There is no builtin mechanism to accomplish what you want.

I concur with the other answers here; normally, we do not change the value of an id column in other rows when a row is deleted. Normally, that id column is a primary key, and ideally, that primary key value is immutable (it is assigned once and it doesn't change.) If it does change, then any references to it will also need to change. (The ON UPDATE CASCADE for a foreign key will propagate the change to a child table, for storage engines like InnoDB that support foreign keys, but not with MyISAM.

Basically, changing an id value causes way more problems than it solves.

There is no "automatic" mechanism that changes the value of a column in other rows when a row is deleted.

With that said, there are times in the development cycle where I have had "static" data, and I wanted control over the id values, and I have made changes to id values. But this is an administrative exercise, not a function performed by an application.