The function insert_Id() returns the last auto-increment number of any table, generated by an insert on a table with an auto-increment column. If no such insertion has occurred or the database does not support the operation, the function returns false.

It is important to remember that there is only a single storage instance for the number, and if one insert statement with an auto-increment number succeeds another, the insert_id value for the second statement will overwrite the value of the first, so retrieve the value of the first before executing the second.

/*
 * Connection assumed
 */
 
/*
 * Insert into table with auto-increment column, current highest value 100
 */
$db->Execute('INSERT INTO monkeys (type) value "arctic"');
$lastId = $db->insert_Id();
print $lastId;
/*
 * returns value 101
 */