LAST_INSERT_ID([expr])
Returns the last automatically-generated value that was set in an AUTO_INCREMENT column. See section 18.4.27
mysql_insert_id().

mysql> select LAST_INSERT_ID();
-> 1

The last ID that was generated is maintained in the server on a per-connection basis. It will not be changed by another client. It will not
even be changed if you update another AUTO_INCREMENT column with a non-magic value (that is, a value that is not NULL and not 0).
If expr is given in an UPDATE clause, then the used value is returned as a last_insert_id value. This can be used to simulate sequences:
First create the table:

create table sequence (id int not null);
insert into sequence values (0);

This can now be used to generate sequence numbers with:

UPDATE sequence SET id=last_insert_id(id+1);

The new id can be read as you would read any normal auto_increment value in MySQL (For example LAST_INSERT_ID() will
return the new id).