if duplicate entry get id - php

Question

My problem in mysql.
My Table name is categories.
CREATE TABLE IF NOT EXISTS `categories` (
`cid` int(10) NOT NULL AUTO_INCREMENT,
`category_name` char(100) DEFAULT NULL,
`parent` int(10) DEFAULT NULL,
PRIMARY KEY (`cid`),
UNIQUE KEY `parent` (`parent`,`category_name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
parent and category_name are unique fields.
If the record not exists I would like to run insert into command.;
select last_insert_id() #get last insert id.
UPDATE
MY PHP Code is:
$sql = "insert into categories (parent,category_name) values ('".$field[parent]."','".$temp->cat_name."')";
if (#$db->query($sql)){
$cid = $db->get_var("select last_insert_id()");
}else{
$cid = $db->get_var("SELECT cid FROM categories WHERE parent=".$field[parent]." and category_name='".$temp->cat_name."'");
}
How can I get exist id return?

Answer 1

If the record not exists I would like to run insert into command.;
You can use INSERT IGNORE ....
INSERT IGNORE INTO `categories` ( `category_name`, `parent` ) values ('A', 1); // will insert it
INSERT IGNORE INTO `categories` ( `category_name`, `parent` ) values ('A', 1); // will ignore it
INSERT IGNORE INTO `categories` ( `category_name`, `parent` ) values ('A', 2); // will insert it
INSERT IGNORE INTO `categories` ( `category_name`, `parent` ) values ('B', 2); // will insert it
INSERT IGNORE INTO `categories` ( `category_name`, `parent` ) values ('B', 2); // will ignore it
From the docs:
If you use the IGNORE keyword, errors that occur while executing the INSERT statement are treated as warnings instead. For example, without IGNORE, a row that duplicates an existing UNIQUE index or PRIMARY KEY value in the table causes a duplicate-key error and the statement is aborted. With IGNORE, the row still is not inserted, but no error is issued.

Answer 2

select last_insert_id()
return a ID after the successful insert. for further processing you can store it in your database after a successful insert.
also you can use insert ignore into .... for avoid duplicate insert

Answer 3

I think this is the best way to do it:
$sql = "insert into categories (parent, category_name) values ('".$field[parent]."','".$temp->cat_name."') ON DUPLICATE KEY UPDATE cid=LAST_INSERT_ID(cid)";
$db->query($sql);
$cid = $db->insert_id;
var_dump($cid);