Question

Let’s have an example:

id (auto_increment)   user
1                     John
2                     Mary
10                    Christopher

How do I force a query to add new users with not used ids? :In our case from 3 to 9:

Answer 1

You could do this with a bit of clever SQL by setting the ID of the record you wish to insert to the first “missing” ID value of the table:

INSERT INTO myTable (id, user) 
VALUES 
(
   (SELECT MIN(mt2.id)+1 from myTable mt2 WHERE NOT EXISTS 
         (SELECT 'Y' from myTable mt3 where mt3.Id = mt2.id + 1)), 
   'New User Name'
)

You may not be able to do this in one query, depending on DBMS. This approach also pretty much renders making the Id column an “auto-generate” column useless; this insert would always find the minimum value that didn’t have an ID, whether that’s the one the identity generator would try to use or not, and you would pretty much always have to enable “identity insert” before inserting to the table, so the auto-gen feature on this table would never be used.