How to obtain the automatic number of the primary key value of the insert data after the mysql insert statement

In the mysql tutorial, how does one obtain the automatic number of the primary key value of the insert statement,

The method is simple. mysql DATA comes with mysql_insert_id (); Function

Usage:

Insert into (A') values ('B ')

$ Nid = mysql_insert_id ();

Method 2:

LAST_INSERT_ID (), but there are many differences between this function and mysql_insert_id (). mysql_insert_id () is to directly obtain the insert_id of the current session, while LAST_INSERT_ID () is an SQL function,
You need to execute the SQL statement to obtain the result, such as: SELECT LAST_INSERT_ID (); obviously, the two effects are the same,
However, it takes a lot of resources to execute an SQL statement. It is much faster to directly obtain the value in memory through mysql_insert_id ().