Question

I am fetching my data with id which is Integer primary key or integer.

But after deleting any row…

After that if we make select query to show all.

But it will give force close because one id is missing.

I want that id can itself take auto increment & decrement.

when i delete a record at the end(i.g. id=7) after this i add a row then id must be 7 not 8. as same when i delete a row in middle(i.g. id=3) then all the row auto specify by acceding.

your idea can help me.

Answer 1

Most systems with auto-incrementing columns keep track of the last value inserted (or the next one to be inserted) and do not ever reissue a number (give the same number twice), even if the last number issued has been removed from the table.

Judging from what you are asking, SQLite is another such system.

If there is any concurrency in the system, then this is risky, but for a single-user, single-app-at-a-time system, you might get away with:

SELECT MAX(id_column) + 1 FROM YourTable

to find the next available value. Depending on how SQLite behaves, you might be able to embed that in the VALUES list of an INSERT statement:

INSERT INTO YourTable(id_column, ...)
    VALUES((SELECT MAX(id_column) + 1 FROM YourTable), ...);

That may not work; you may have to do this as two operations. Note that if there is any concurrency, the two statement form is a bad idea^TM. The primary key unique constraint normally prevents disaster, but one of two concurrent statements fails because it tries to insert a value that the other just inserted – so it has to retry and hope for the best. Clearly, a cell phone has less concurrency than, say, a web server so the problem is correspondingly less severe. But be careful.

On the whole, though, it is best to let gaps appear in the sequence without worrying about it. It is usually not necessary to worry about them. If you must worry about gaps, don’t let people make them in the first place. Or move an existing row to fill in the gap when you do a delete that creates one. That still leaves deletes at the end creating gaps when new rows are added, which is why it is best to get over the “it must be a contiguous sequence of numbers” mentality. Auto-increment guarantees uniqueness; it does not guarantee contiguity.