PHP returns the id generated by insert operation_PHP tutorial

Sometimes you need to know the ID generated after performing an INSERT operation in the database (I use MySQL, the primary key is set to AUTO_INCREMENT, when performing the insert operation, you do not need to specify the value of the ID and it is generated by the database itself) , then you can use the PHP function mysql_insert_id() to directly obtain the ID, which is very convenient.

But one thing is that if the value of the ID column with the AUTO_INCREMENT attribute is clearly pointed out in the INSERT statement, then the function will return 0 because the ID value is specified by the user and is not automatically generated by the database.

The PHP manual describes this function as follows:

mysql_insert_id()

The mysql_insert_id() function returns the ID generated by the previous INSERT operation. If the previous query did not produce an AUTO_INCREMENT ID, mysql_insert_id() returns 0.

Syntax: mysql_insert_id(connection)

Parameter connection, optional. Specifies the MySQL connection. If not specified, the previous connection is used.

mysql_insert_id() returns the ID number of the AUTO_INCREMENT generated in the previous INSERT query in the given connection. If connection is not specified, the last open connection is used.

If you need to save the value for later use, be sure to call mysql_insert_id() immediately after the query that produced the value.

<?php
$con = mysql_connect("localhost", "hello", "321");
if (!$con)
{
	die('Could not connect: ' . mysql_error());
}
$db_selected = mysql_select_db("test_db",$con);
$sql = "INSERT INTO person VALUES ('Carter','Thomas','Beijing')";
$result = mysql_query($sql,$con);
echo "ID of last inserted record is: " . mysql_insert_id();
mysql_close($con);
?>

mysql_insert_id() returns the ID number of the AUTO_INCREMENT generated in the previous INSERT query in the given link_identifier. If link_identifier is not specified, the last opened connection is used. If the previous query did not produce a value for AUTO_INCREMENT, mysql_insert_id() returns 0. If you need to save the value for later use, be sure to call mysql_insert_id() immediately after the query that produced the value.

LAST_INSERT_ID()

MySQL also provides an API with the same function. It always saves the latest AUTO_INCREMENT value and will not be reset between query statements. That is to say, after executing the INSERT operation, execute SELECT, Neither UPDATE nor DELETE statements will affect the return value of this API.

You can use SELECT LAST_INSERT_ID(); to query the return value of LAST_INSERT_ID().

Use a single INSERT statement to insert multiple records. LAST_INSERT_ID() only returns the AUTO_INCREMENT value generated by the first record inserted.