Question

I have a table which contains a unique integer field containing consecutive values. When I try to increment these values using the method below I violate the unique constraint. Is there a method for doing this successfully?

CREATE TABLE numbers(num INT UNIQUE NOT NULL)
UPDATE numbers SET num=num+1

Answer 1

This has to be a bug. It obviously won’t induce a constraint violation, and it works in SQL Server. In fact, I am quite certain it is a bug, since I can make it succeed if I insert the numbers in descending order:

sqlite> INSERT INTO numbers (num) VALUES (3);
sqlite> INSERT INTO numbers (num) VALUES (2);
sqlite> INSERT INTO numbers (num) VALUES (1);
sqlite> UPDATE numbers SET num = num + 1;
sqlite> SELECT * FROM numbers;
4
3
2

The correctness of an UPDATE should not depend on the order of rows in the table.

As a simple work-around, you could do this:

UPDATE numbers SET num = -num;
UPDATE numbers SET num = 1 - num;