Finding the next available id in MySQL

Question

I have to find the next available id (if there are 5 data in database, I have to get the next available insert place which is 6) in a MySQL database. How can I do that? I h

Answer 1

If you really want to compute the key of the next insert before inserting the row (which is in my opinion not a very good idea), then I would suggest that you use the maximum currently used id plus one:

SELECT MAX(id) + 1 FROM table

But I would suggest that you let MySQL create the id itself (by using a auto-increment column) and using LAST_INSERT_ID() to get it from the DBMS. To do this, use a transaction in which you execute the insert and then query for the id like:

INSERT INTO table (col1) VALUES ("Text");
SELECT LAST_INSERT_ID();

The returnset now contains only one column which holds the id of the newly generated row.

Answer 2

It's too late to answer this question now, but hope this helps someone.

@Eimantas has already given the best answer but the solution won't work if you have two or more tables by the same name under the same server.

I have slightly modified @Eimantas's answer to tackle the above problem.

select Auto_increment as id from information_schema.tables where table_name = 'table_name' and table_schema = 'database_name'

Answer 3

This worked well for me (MySQL 5.5), also solving the problem of a "starting" position.

SELECT
    IF(res.nextID, res.nextID, @r) AS nextID
FROM
    (SELECT @r := 30) AS vars,
    (
    SELECT MIN(t1.id + 1) AS nextID
    FROM test t1
    LEFT JOIN test t2
      ON t1.id + 1 = t2.id
    WHERE t1.id >= @r
      AND t2.id IS NULL
      AND EXISTS (
          SELECT id
          FROM test
          WHERE id = @r
      )
  LIMIT 1
  ) AS res
LIMIT 1

As mentioned before these types of queries are very slow, at least in MySQL.