小弟我的表P_id没设置为自动增长，插入数据时小弟我要通过程序控制p_id自动增长，该如何做。求教

//添加商品SQL
	mysql_query("insert into t_product
	(
	p_id
	categorycode,
	subcategorycode,
	price,
	shopid
	)
	values
	(
	
	'$categorycode',
	'$subcategorycode',
	'$price',
	$s_id
	)");

	

list($pid) = mysql_fetch_row(mysql_query("select max(p_id)+1 from t_product"));
//添加商品SQL
    mysql_query("insert into t_product
    (
    p_id
    categorycode,
    subcategorycode,
    price,
    shopid
    )
    values
    (
     '$p_id',
    '$categorycode',
    '$subcategorycode',
    '$price',
    $s_id
    )");