[mysql] SELECT last id, without INSERT

I'm trying to retrieve the id of one table A to insert into another table B. I cannot use last_insert_id() as i have not inserted anything into A. Any ideas on how to do this nicely?

$n = mysql_query("SELECT max(id) FROM tablename"); doesn't seem to work, nor does

$n = mysql_query("SELECT max(id) FROM tablename GROUP BY id");

You could descendingly order the tabele by id and limit the number of results to one:

SELECT id FROM tablename ORDER BY id DESC LIMIT 1

BUT: ORDER BY rearranges the entire table for this request. So if you have a lot of data and you need to repeat this operation several times, I would not recommend this solution.

I have different solution:

SELECT AUTO_INCREMENT - 1 as CurrentId FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'dbname' AND TABLE_NAME = 'tablename'

You can get maximum column value and increment it:

InnoDB uses the following algorithm to initialize the auto-increment counter for a table t that contains an AUTO_INCREMENT column named ai_col: After a server startup, for the first insert into a table t, InnoDB executes the equivalent of this statement:

SELECT MAX(ai_col) FROM t FOR UPDATE;

InnoDB increments by one the value retrieved by the statement and assigns it to the column and to the auto-increment counter for the table. If the table is empty, InnoDB uses the value 1.

Also you can use SHOW TABLE STATUS and its "Auto_increment" value.

I think to add timestamp to every record and get the latest. In this situation you can get any ids, pack rows and other ops.