Problem with MySql INSERT MAX()+1

Question

I have a single table containing many users. In that table I have column called user_id (INT), which I want increment separately for each person. user_id MUST start at 1

I've prepared a simple example:

Showing all names
+--------------+-----------------------+
| user_id      | name                  |
+--------------+-----------------------+
| 1            | Bob                   |
| 1            | Marry                 |
| 2            | Bob                   |
| 1            | John                  |
| 3            | Bob                   |
| 2            | Marry                 |
+--------------+-----------------------+


Showing only where name = Bob
+--------------+-----------------------+
| user_id      | name                  |
+--------------+-----------------------+
| 1            | Bob                   |
| 2            | Bob                   |
| 3            | Bob                   |
+--------------+-----------------------+

The following query will do this, but it will only work if 'Bob' already exists in the table...

INSERT INTO users(user_id, name) SELECT(SELECT MAX(user_id)+1 from users where 
name='Bob'), 'Bob';

If Bob does not exist (first entry) user_id is set to 0 (zero). This is the problem. I need the user_id to start from 1 not 0.

Answer 1

It's been reported as a bug in MySQL.

I'm quoting Guilhem Bichot:

Second, here is the simplest of workarounds:
instead of using:
insert into foo(lfd) values((select max(lfd) from foo)+1)
just do
insert into foo(lfd) select (max(lfd)+1) from foo;

Answer 2

You can use something like this:

INSERT INTO users (user_id, name)
SELECT 1 + coalesce((SELECT max(user_id) FROM users WHERE name='Bob'), 0), 'Bob';

But such query can lead to a race condition. Make sure you are in a transaction and you lock the users table before running it. Otherwise you might end up with two Bobs with the same number.

Answer 3

Don't use MAX() + 1 then. Use an auto-numbering scheme on the table.

I didn't read the question properly. Use Greg's suggestion of IFNULL().

Answer 4

You can use IFNULL:

INSERT INTO users(user_id, name)
SELECT(IFNULL((SELECT MAX(user_id)+1 from users where name='Bob'), 1), 'Bob';