How to get the primary key value AutoNumber for insert data after MySQL INSERT statement

How do I get the primary key value AutoNumber for the insert data after the MySQL tutorial insert statement?

The method is very simple, the MySQL data with the mysql_insert_id ();

How to use:

Insert INTO (a ') VALUES (' B ')

$nid = mysql_insert_id ();

Method Two:

LAST_INSERT_ID (), but there is a lot of difference about this function compared to mysql_insert_id (), mysql_insert_id () is the insert_id that gets the current session directly, and last_insert_id () is a SQL function,
Needs to be obtained by executing SQL, such as SELECT last_insert_id (); Obviously the two effects are the same,
But it takes a lot of resources to execute SQL once, and it's much faster to get the value in memory directly via MYSQL_INSERT_ID ()