mysql_insert_id（）的行为

Question

I am using functions from a php library that uses mysql_insert_id() every now and then. Now I've modified a few functions that insert data into tables such that the primary key value is explicitly specified e.g. I insert an a row with ID=300 followed by a row with ID=200 when the table originally had 10 rows. I am wondering if mysql_insert_id will behave as expected i.e. return the value I explicitly specified for the AUTO_INCREMENT PRIMARY KEY column.

Answer 1

Table:

CREATE TABLE `foo` (
  `id` int(11) NOT NULL auto_increment,
  `value` varchar(32) NOT NULL,
  PRIMARY KEY  (`id`)
) ;

Code:

print phpversion()."
";
mysql_connect('localhost','user','pass');
mysql_select_db('database');

mysql_query('INSERT INTO `foo` (`id`,`value`) VALUES(100,"bar")');
print var_export(mysql_insert_id())."
";

mysql_query('INSERT INTO `foo` (`value`) VALUES("zoid")');
print var_export(mysql_insert_id())."
";

mysql_query('INSERT INTO `foo` (`id`,`value`) VALUES(99,"yargh")');
print var_export(mysql_insert_id())."
";

$q = mysql_query('SHOW TABLE STATUS LIKE "foo"');
$status = mysql_fetch_assoc($q);
mysql_free_result($q);
print $status['Auto_increment']."
";

mysql_query('INSERT INTO `foo` (`value`) VALUES("whatever")');
print var_export(mysql_insert_id())."
";

Output:

5.2.XX-0.dotdeb.1
100
101
99
102
102

TL/DR version: it returns the last id, be it auto incremented, or explicitly given.

UPDATE: Added INSERT with id < 100, as suggested by Mchl.