พอดียังไม่กระจ่างเลยต้องมาถามกันใหม่ในเรื่อง select max(id) from .... กับ mysql_insert_id

CREATE TABLE MyTable (
     ID INT NOT NULL AUTO_INCREMENT,
     MyCode VARCHAR(8) NOT NULL,
     MyWebsite VARCHAR(32),
     PRIMARY KEY (ID)
);

INSERT INTO MyTable (
     MyCode,
     MyWebsite
) VALUES (
     CONCAT('CODE', LPAD(CONVERT((SELECT AUTO_INCREMENT
          FROM information_schema.tables 
          WHERE table_name='mytable'
          AND table_schema = DATABASE()), CHAR(16)), 4, '0')),
     'Thaicreate'
);

DELETE FROM MyTable
WHERE ID = 7;

<?php

$sql = "INSERT INTO my_table ................... ";

$insert_id = mysql_insert_id();

$sql = "SELECT COUNT(*) AS max_number FROM my_table 
            WHERE my_year = '2557' AND id_auto < $insert_id";

?>

$today = date('Y-m-d');
$next_year = date('Y').'-01-01';
$next_year = date('Y-m-d', strtotime($next_year));

#------ หา id_want -------#
if($today==$next_year){ #ถ้าใช้ก็ให้ id_want เท่ากับ 1
   $id_want = '1';
} else {
   #ดึงข้อมูล id_want ล่าสุดจาก DB 
   $getID = mysql_query("SELECT id_want FROM xx ORDER BY id_auto DESC LIMIT 1 ");
   $resultID = mysql_fetch_assoc($getID);
   
   #ค่า id_want ที่ได้เพื่อเอาไปบันทึกต่อไป
   $id_want = $resultID['id_want']+1;
}
#------ จบหา id_want -------#

INSERT INTO xx(id_want) VALUES ($id_want);